Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q5

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q5

[Mark_H_Johnson]

>i've uploaded -Q5 to:
> [snip the rest...]

Thanks.

This appears to be the first 2.6.x kernel I've run that has results
comparable to 2.4.x kernels with low latency patches and kernel preemption.
The few remaining symptoms I see include:

 - a few long (> 1 msec) delays in the real time CPU loop (no system calls)
 - varying time to complete the write system call (for audio) - much
different than 2.4
 - a couple latency traces (> 700 usec) in the network driver

For reference, these tests were performed on the following SMP system:
  Dual 866 Mhz Pentium III
  512 Mbyte memory
  IDE system disk (DMA enabled)
The basic test is Benno's latency test
(http://www.gardena.net/benno/linux/audio) with some slight modifications
to the tests to keep the second CPU busy (non real time CPU burner) and to
add network I/O tests. The 2.4 tests were run with 2.4.20, the 2.6 tests
were run with 2.4.9-rc1-Q5. On 2.6, voluntary_preemption,
kernel_preemption, hardirq_preemption, and softirq_preemption are all 1. I
also set
  /sys/block/hda/queue/max_sectors_kb = 32
  /sys/block/hda/queue/read_ahead_kb = 32
  /proc/sys/net/core/netdev_max_backlog = 8
and the audio driver was set to be non-threaded.

BASIC RESULTS
=============
Comparison of results between 2.6.x and 2.4.x; values in milliseconds.
Nominal values for the write operation is 1.45 msec; the CPU loop is 1.16
msec.

          Max CPU Delta     Max Write Delta
Test     2.4.x     2.6.x    2.4.x     2.6.x
X11       0.10      0.16     0.05      0.65
/proc     0.07      0.17     0.05      0.65
net out   0.15      0.19     0.05      0.75
net in    0.17      0.23     0.05      0.95
dsk wrt   0.49      0.18     0.25      1.05
dsk copy  2.48      0.68     2.25      1.25
disk rd   3.03      1.61     2.75      1.35

LONG DELAYS
===========

Note I still see over 110% worst case overhead on a max priority real time
CPU task (no system calls) when doing heavy disk I/O on 2.6. It is much
better than 2.4, but still disturbing. What I would hope would happen on a
dual CPU system like mine, is that the real time task tends to be on one
CPU and the other system activity would tend to stay on the other CPU.
However, the results do not seem to indicate that behavior.

VARYING SYSTEM CALL TIMES
=========================

In 2.4, it appears that the duration of the write system call is basically
fixed and dependent on the duration of the audio fragment. In 2.6, this
behavior is now different. If I look at the chart in detail, it appears the
system is queueing up several write operations during the first few seconds
of testing. You can see this by consistently low elapsed times for the
write system call. Then the elapsed time for the write bounces up / down in
a sawtooth pattern over a 1 msec range. Could someone explain the cause of
this new behavior and if there is a setting to restore the old behavior? I
am concerned that this queueing adds latency to audio operations (when
trying to synchronize audio with other real time behavior).

LONG NETWORK LATENCIES
======================

In about 25 minutes of heavy testing, I had two latency traces with
/proc/sys/kernel/preempt_max_latency set to 700. They had the same start /
end location with the long delay as follows:
  730 us, entries: 361
  ...
  started at rtl8139_poll+0x3c/0x160
  ended at   rtl8139_poll+0x100/0x160
  00000001 0.000ms (+0.000ms): rtl8139_poll (net_rx_action)
  00000001 0.140ms (+0.140ms): rtl8139_rx (rtl8139_poll)
  00000001 0.556ms (+0.416ms): alloc_skb (rtl8139_rx)
  ... remaining items all > +0.005ms ...

  731 us, entries: 360
  ...
  started at rtl8139_poll+0x3c/0x160
  ended at   rtl8139_poll+0x100/0x160
  00000001 0.000ms (+0.000ms): rtl8139_poll (net_rx_action)
  00000001 0.000ms (+0.000ms): rtl8139_rx (rtl8139_poll)
  00000001 0.002ms (+0.001ms): alloc_skb (rtl8139_rx)
  00000001 0.141ms (+0.139ms): kmem_cache_alloc (alloc_skb)
  00000001 0.211ms (+0.070ms): __kmalloc (alloc_skb)
  00000001 0.496ms (+0.284ms): eth_type_trans (rtl8139_rx)
  00000001 0.565ms (+0.068ms): netif_receive_skb (rtl8139_rx)
  ... remaining items all > +0.005ms ...

Still much better than my previous results (before setting
netdev_max_backlog).

I will be running some additional tests
 - reducing preempt_max_latency
 - running with sortirq and hardirq_preemption=0
to see if these uncover any further problems.

Thanks again for the good work.
--Mark H Johnson
  <mailto:Mark_H_Johnson@raytheon.com>

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q5

[Ingo Molnar]

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* Mark_H_Johnson@raytheon.com <Mark_H_Johnson@raytheon.com> wrote:

> LONG NETWORK LATENCIES
> ======================
> 
> In about 25 minutes of heavy testing, I had two latency traces with
> /proc/sys/kernel/preempt_max_latency set to 700. They had the same start /
> end location with the long delay as follows:
>   730 us, entries: 361
>   ...
>   started at rtl8139_poll+0x3c/0x160
>   ended at   rtl8139_poll+0x100/0x160

regarding this particular latency, could you try the attached patch
ontop of -Q5? It turns the ->poll() loop into separate, individually
preemptable iterations instead of one batch of processing. In theory
this should result in latency being lower regardless of the
netdev_max_backlog value.

	Ingo

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--- linux/net/core/dev.c.orig2	
+++ linux/net/core/dev.c	
@@ -1903,7 +1903,7 @@ static void net_rx_action(struct softirq
 {
 	struct softnet_data *queue = &__get_cpu_var(softnet_data);
 	unsigned long start_time = jiffies;
-	int budget = netdev_max_backlog;
+	int budget = netdev_max_backlog, loops;
 
 	
 	local_irq_disable();
@@ -1926,7 +1926,10 @@ static void net_rx_action(struct softirq
 		dev = list_entry(queue->poll_list.next,
 				 struct net_device, poll_list);
 
-		if (dev->quota <= 0 || dev->poll(dev, &budget)) {
+		loops = 1;
+		if (dev->quota <= 0 || dev->poll(dev, &loops)) {
+			if (loops < 1)
+				budget--;
 			local_irq_disable();
 			list_del(&dev->poll_list);
 			list_add_tail(&dev->poll_list, &queue->poll_list);

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q5

[Ingo Molnar]

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* Mark_H_Johnson@raytheon.com <Mark_H_Johnson@raytheon.com> wrote:

> VARYING SYSTEM CALL TIMES
> =========================
> 
> In 2.4, it appears that the duration of the write system call is
> basically fixed and dependent on the duration of the audio fragment.
> In 2.6, this behavior is now different. If I look at the chart in
> detail, it appears the system is queueing up several write operations
> during the first few seconds of testing. You can see this by
> consistently low elapsed times for the write system call. Then the
> elapsed time for the write bounces up / down in a sawtooth pattern
> over a 1 msec range. Could someone explain the cause of this new
> behavior and if there is a setting to restore the old behavior? I am
> concerned that this queueing adds latency to audio operations (when
> trying to synchronize audio with other real time behavior).

since the latency tracer does not trigger, we need a modified tracer to
find out what's happening during such long delays. I've attached the
'user-latency-tracer' patch ontop of -Q5, which is a modification of the
latency tracer. This patch enables free-running tracing which includes
all kernel functions not just critical sections. To activate this, two
things have to be done. Firstly:

	echo 2 > /proc/sys/kernel/trace_enabled

this turns off the normal latency tracer and turns on the 'user tracer'. 
Traces can be generated by userspace via a hack done to
sys_gettimeofday():

	gettimeofday(0,1); // enable the tracer
	gettimeofday(0,0); // save current trace and disable the tracer

this way the tracing can be limited to the suspected codepaths only.

could you try to insert gettimeofday(0,1) into your testsuite just
before the write() call is done, and right after the write() call, and
save a couple of representative traces? The patch also ups the # of
latency entries to 8000 - if that is still insufficient then please
increase it as needed.

NOTE: on SMP the tracing on/off is strictly per-CPU. So do the enabling
and disabling of the trace on the same CPU. (doing otherwise wont cause
problems, but the generated traces will be less useful.)

	Ingo

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--- linux/kernel/latency.c.orig
+++ linux/kernel/latency.c
@@ -27,7 +27,7 @@ static DECLARE_MUTEX(max_mutex);
 
 #ifdef CONFIG_LATENCY_TRACE
 
-#define MAX_TRACE 4000UL
+#define MAX_TRACE 8000UL
 
 struct trace_entry {
 	unsigned long preempt_count;
@@ -63,14 +63,13 @@ static unsigned long max_nice;
 static unsigned long max_policy;
 static unsigned long max_rt_priority;
 
-inline void notrace
+static inline void notrace
 ____trace(struct cpu_trace *tr, unsigned long eip, unsigned long parent_eip)
 {
 	struct trace_entry *entry;
 
-	BUG_ON(!irqs_disabled());
-
-	if (tr->trace_idx < MAX_TRACE) {
+	if ((tr->critical_start || (trace_enabled == 2)) &&
+			(tr->trace_idx < MAX_TRACE)) {
 		entry = tr->trace + tr->trace_idx;
 		entry->eip = eip;
 		entry->parent_eip = parent_eip;
@@ -80,7 +79,7 @@ ____trace(struct cpu_trace *tr, unsigned
 	tr->trace_idx++;
 }
 
-inline void notrace
+static inline void notrace
 ___trace(unsigned long eip, unsigned long parent_eip)
 {
 	unsigned long flags;
@@ -266,6 +265,18 @@ static int setup_preempt_thresh(char *s)
 }
 __setup("preempt_thresh=", setup_preempt_thresh);
 
+static void update_max_trace(struct cpu_trace *tr)
+{
+	memcpy(&max_trace, tr, sizeof (max_trace));
+
+	memcpy(max_comm, current->comm, 16);
+	max_pid = current->pid;
+	max_uid = current->uid;
+	max_nice = current->static_prio - 20 - MAX_RT_PRIO;
+	max_policy = current->policy;
+	max_rt_priority = current->rt_priority;
+}
+
 static void notrace check_preempt_timing(struct cpu_trace *tr)
 {
 #ifdef CONFIG_LATENCY_TRACE
@@ -274,6 +285,10 @@ static void notrace check_preempt_timing
 	unsigned long parent_eip = (unsigned long)__builtin_return_address(1);
 	unsigned long latency;
 
+#ifdef CONFIG_LATENCY_TRACE
+	if (trace_enabled == 2)
+		return;
+#endif
 	atomic_inc(&tr->disabled);
 	latency = cycles_to_usecs(get_cycles() - tr->preempt_timestamp);
 
@@ -293,14 +308,7 @@ static void notrace check_preempt_timing
 
 #ifdef CONFIG_LATENCY_TRACE
 	____trace(tr, eip, parent_eip);
-	memcpy(&max_trace, tr, sizeof (max_trace));
-
-	memcpy(max_comm, current->comm, 16);
-	max_pid = current->pid;
-	max_uid = current->uid;
-	max_nice = current->static_prio - 20 - MAX_RT_PRIO;
-	max_policy = current->policy;
-	max_rt_priority = current->rt_priority;
+	update_max_trace(tr);
 #endif
 
 	if (preempt_thresh)
@@ -354,6 +362,10 @@ void notrace add_preempt_count(int val)
 #endif
 
 	preempt_count() += val;
+#ifdef CONFIG_LATENCY_TRACE
+	if (trace_enabled == 2)
+		return;
+#endif
 	if (preempt_count() == val) {
 		struct cpu_trace *tr = &__get_cpu_var(trace);
 
@@ -383,3 +395,27 @@ void notrace sub_preempt_count(int val)
 	preempt_count() -= val;
 }
 EXPORT_SYMBOL(sub_preempt_count);
+
+void user_trace_start(void)
+{
+	struct cpu_trace *tr;
+
+	if (trace_enabled != 2)
+		return;
+	tr = &get_cpu_var(trace);
+	tr->trace_idx = 0;
+	mcount();
+	put_cpu_var(trace);
+}
+
+void user_trace_stop(void)
+{
+	struct cpu_trace *tr;
+
+	if (trace_enabled != 2)
+		return;
+	tr = &get_cpu_var(trace);
+	mcount();
+	update_max_trace(tr);
+	put_cpu_var(trace);
+}
--- linux/kernel/time.c.orig2	
+++ linux/kernel/time.c	
@@ -90,8 +90,17 @@ asmlinkage long sys_stime(time_t __user 
 
 #endif /* __ARCH_WANT_SYS_TIME */
 
+extern void user_trace_start(void);
+extern void user_trace_stop(void);
+
 asmlinkage long sys_gettimeofday(struct timeval __user *tv, struct timezone __user *tz)
 {
+#ifdef CONFIG_LATENCY_TRACE
+	if (!tv && ((int)tz == 1))
+		user_trace_start();
+	if (!tv && !tz)
+		user_trace_stop();
+#endif
 	if (likely(tv != NULL)) {
 		struct timeval ktv;
 		do_gettimeofday(&ktv);

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q5 - netdev_max_back_log is too small

[P.O. Gaillard]

Hello,

I know that you have reduced netdev_max_back_log to 8 to reduce the latency. But 
I think that you should know that I had to set it back to 32 to avoid ethernet 
frame losses on a 3GHz P4 using e1000 (eth0/threaded=1).

My app is still the one with a 20Mbytes/s flow of data and some signal 
processing work. That's only 20% of max Gigabit Ethernet load and 40% of CPU 
time. Not really hot stuff.

So, this were my 2 cents to help you decide how to balance latency and 
throughput. I hope that you can find a good balance or find a way to allow 
people to easily choose their own balance (e.g. maybe there should be a list of 
parameters impacting latency in the Documentation directory).

  please keep on the good work and thanks a lot !

	P.O. Gaillard

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q5 - netdev_max_back_log is too small

[Ingo Molnar]

* P.O. Gaillard <pierre-olivier.gaillard@fr.thalesgroup.com> wrote:

> I know that you have reduced netdev_max_back_log to 8 to reduce the
> latency. But I think that you should know that I had to set it back to
> 32 to avoid ethernet frame losses on a 3GHz P4 using e1000
> (eth0/threaded=1).

could you try the -Q6 patch? That leaves netdev_max_backlog at the
default value of 300 and uses another method to break up the networking
codepaths, without any bad tradeoffs.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q5

[Ingo Molnar]

* Mark_H_Johnson@raytheon.com <Mark_H_Johnson@raytheon.com> wrote:

> In 2.4, it appears that the duration of the write system call is
> basically fixed and dependent on the duration of the audio fragment.
> In 2.6, this behavior is now different. If I look at the chart in
> detail, it appears the system is queueing up several write operations
> during the first few seconds of testing. You can see this by
> consistently low elapsed times for the write system call. Then the
> elapsed time for the write bounces up / down in a sawtooth pattern
> over a 1 msec range. Could someone explain the cause of this new
> behavior and if there is a setting to restore the old behavior? I am
> concerned that this queueing adds latency to audio operations (when
> trying to synchronize audio with other real time behavior).

i think i found the reason for the sawtooth: it's a bug in hardirq
redirection. In certain situations we can end up not waking up softirqd,
resulting in a random 0-1msec latency between hardirq arrival and
softirq execution. We dont see higher latencies because timer IRQs
always wake up softirqd which hides the bug to a certain degree.

I'll fix this in -Q8.

	Ingo

[patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Ingo Molnar]

i've released the -Q8 patch:

  http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-Q8

ontop of:

  http://redhat.com/~mingo/voluntary-preempt/diff-bk-040828-2.6.8.1.bz2

this release fixes an artificial 0-1msec delay between hardirq arrival
and softirq invocation. This should solve some of the ALSA artifacts
reported by Mark H Johnson. It should also solve the rtl8139 problems -
i've put such a card into a testbox and with -Q7 i had similar packet
latency problems while with -Q8 it works just fine.

So netdev_backlog_granularity is still a value of 1 in -Q8, please check
whether the networking problems (bootup and service startup and latency)
problems are resolved. (and increase this value in case there are still
problems.)

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Lee Revell]

On Thu, 2004-09-02 at 02:55, Ingo Molnar wrote:
> i've released the -Q8 patch:
> 
>   http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-Q8
> 
> ontop of:
> 
>   http://redhat.com/~mingo/voluntary-preempt/diff-bk-040828-2.6.8.1.bz2
> 

Here are traces of a 145, 190, and 217 usec latencies in
netif_receive_skb:

http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace2.txt
http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace3.txt
http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace4.txt

Some of these are with ip_conntrack enabled, at the request of another
poster, this does not make much of a difference, it increases the worst
case latency by 20 usec or so.

Also there is the rt_garbage_collect issue, previously reported.  I have
not seen this lately but I do not remember seeing that it was fixed.

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Ingo Molnar]

* Lee Revell <rlrevell@joe-job.com> wrote:

> Here are traces of a 145, 190, and 217 usec latencies in
> netif_receive_skb:
> 
> http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace2.txt
> http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace3.txt
> http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace4.txt

these all seem to be single-packet processing latencies - it would be
quite hard to make those codepaths preemptible.

i'd suggest to turn off things like netfilter and ip_conntrack (and
other optional networking features that show up in the trace), they can
only increase latency:

 00000001 0.016ms (+0.000ms): ip_rcv (netif_receive_skb)
 00000001 0.019ms (+0.002ms): nf_hook_slow (ip_rcv)
 00000002 0.019ms (+0.000ms): nf_iterate (nf_hook_slow)
 00000002 0.021ms (+0.001ms): ip_conntrack_defrag (nf_iterate)
 00000002 0.022ms (+0.000ms): ip_conntrack_in (nf_iterate)
 00000002 0.022ms (+0.000ms): ip_ct_find_proto (ip_conntrack_in)
 00000103 0.023ms (+0.000ms): __ip_ct_find_proto (ip_ct_find_proto)
 00000102 0.024ms (+0.000ms): local_bh_enable (ip_ct_find_proto)
 00000002 0.025ms (+0.001ms): tcp_error (ip_conntrack_in)

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Ingo Molnar]

* Lee Revell <rlrevell@joe-job.com> wrote:

> Also there is the rt_garbage_collect issue, previously reported.  I
> have not seen this lately but I do not remember seeing that it was
> fixed.

i dont think it's fixed, please re-report it if it occurs again, there
have been many changes.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Lee Revell]

On Thu, 2004-09-02 at 03:15, Ingo Molnar wrote:
> * Lee Revell <rlrevell@joe-job.com> wrote:
> 
> > Here are traces of a 145, 190, and 217 usec latencies in
> > netif_receive_skb:
> > 
> > http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace2.txt
> > http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace3.txt
> > http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace4.txt
> 
> these all seem to be single-packet processing latencies - it would be
> quite hard to make those codepaths preemptible.
> 

I suspected as much, these are not a problem.  The large latencies from
reading the /proc filesystem are a bit worrisome (trace1.txt), I will
report these again if they still happen with Q8.

Lee 

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Ingo Molnar]

* Lee Revell <rlrevell@joe-job.com> wrote:

> > these all seem to be single-packet processing latencies - it would be
> > quite hard to make those codepaths preemptible.
> 
> I suspected as much, these are not a problem.  The large latencies
> from reading the /proc filesystem are a bit worrisome (trace1.txt), I
> will report these again if they still happen with Q8.

conntrack's ct_seq ops indeed seems to have latency problems - the quick
workaround is to disable conntrack.

The reason for the latency is that ct_seq_start() does a read_lock() on
ip_conntrack_lock and only ct_seq_stop() releases it - possibly
milliseconds later. But the whole conntrack /proc code is quite flawed:

        READ_LOCK(&ip_conntrack_lock);

        if (*pos >= ip_conntrack_htable_size)
                return NULL;

        bucket = kmalloc(sizeof(unsigned int), GFP_KERNEL);
        if (!bucket) {
                return ERR_PTR(-ENOMEM);
        }
        *bucket = *pos;
        return bucket;

#1: we kmalloc(GFP_KERNEL) with a spinlock held and softirqs off - ouch!

#2: why does it do the kmalloc() anyway? It could store the position in
    the seq pointer just fine. No need to alloc an integer pointer to
    store the value in ...

#3: to fix the latency, ct_seq_show() could take the ip_conntrack_lock 
    and could check the current index against ip_conntrack_htable_size. 
    There's not much point in making this non-preemptible, there's 
    a 4K granularity anyway.

Rusty, what's going on in this code?

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[mika.penttila]

Ingo,

I think there might be a problem with voluntary-preempt's hadling of softirqs. Namely, in cond_resched_softirq(), you do __local_bh_enable() and local_bh_disable(). But it may be the case that the softirq is handled from ksoftirqd, and then the preempt_count isn't elevated with SOFTIRQ_OFFSET (only PF_SOFTIRQ is set). So the __local_bh_enable() actually makes preempt_count negative, which might have bad effects. Or am I missing something?

Mika

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Ingo Molnar]

* Ingo Molnar <mingo@elte.hu> wrote:

> this release fixes an artificial 0-1msec delay between hardirq arrival
> and softirq invocation. This should solve some of the ALSA artifacts
> reported by Mark H Johnson. It should also solve the rtl8139 problems
> - i've put such a card into a testbox and with -Q7 i had similar
> packet latency problems while with -Q8 it works just fine.

the rtl8139 problems are not fixed yet - i can still reproduce the
delayed packet issues.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Ingo Molnar]

* mika.penttila@kolumbus.fi <mika.penttila@kolumbus.fi> wrote:

> Ingo,
> 
> I think there might be a problem with voluntary-preempt's hadling of
> softirqs. Namely, in cond_resched_softirq(), you do
> __local_bh_enable() and local_bh_disable(). But it may be the case
> that the softirq is handled from ksoftirqd, and then the preempt_count
> isn't elevated with SOFTIRQ_OFFSET (only PF_SOFTIRQ is set). So the
> __local_bh_enable() actually makes preempt_count negative, which might
> have bad effects. Or am I missing something?

you are right. Fortunately the main use of cond_resched_softirq() is via
cond_resched_all() - which is safe because it uses softirq_count(). But
the kernel/timer.c explicit call to cond_resched_softirq() is unsafe.
I've fixed this in my tree and i've added an assert to catch the
underflow when it happens.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Peter Zijlstra]

On Thu, 2004-09-02 at 10:32, Ingo Molnar wrote:
> * mika.penttila@kolumbus.fi <mika.penttila@kolumbus.fi> wrote:
> 
> > Ingo,
> > 
> > I think there might be a problem with voluntary-preempt's hadling of
> > softirqs. Namely, in cond_resched_softirq(), you do
> > __local_bh_enable() and local_bh_disable(). But it may be the case
> > that the softirq is handled from ksoftirqd, and then the preempt_count
> > isn't elevated with SOFTIRQ_OFFSET (only PF_SOFTIRQ is set). So the
> > __local_bh_enable() actually makes preempt_count negative, which might
> > have bad effects. Or am I missing something?
> 
> you are right. Fortunately the main use of cond_resched_softirq() is via
> cond_resched_all() - which is safe because it uses softirq_count(). But
> the kernel/timer.c explicit call to cond_resched_softirq() is unsafe.
> I've fixed this in my tree and i've added an assert to catch the
> underflow when it happens.
> 
> 	Ingo

I've had linux-2.6.9-rc1-bk8-Q7 lock up on me this morning not long
after starting a glibc compile resulting from: emerge -uo gnome
although it did survive a make World on xorg-cvs.

Could this have been caused by the bug under discussion?

Unfortunatly I don't have much testing time before I go on hollidays,
so for now I went back to linux-2.6.9-rc1-bk6-Q5 which on my machine is
rock solid.

Peter

[patch] voluntary-preempt-2.6.9-rc1-bk4-Q9

[Ingo Molnar]

i've released the -Q9 patch:

  http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-Q9

ontop of:

  http://redhat.com/~mingo/voluntary-preempt/diff-bk-040828-2.6.8.1.bz2

Changes:

 - fixed the cond_resched_softirq() bug noticed by Mika Penttila.

 - updated the preemption-friendly network-RX code but 8193too.c still
   produces delayed packets so netdev_backlog_granularity now defaults
   to 2, which seems to be working fine on my testbox.

 - the latency_trace output now includes the kernel and patch version,
   for easier sorting of reports.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q6 - network is no longer smooth

[P.O. Gaillard]

Hello,

I just tried with Q6 and the network behaviour seems odd :
  - my ssh connection freezes a bit,
  - communication between the two PCs sharing the GigE connection is difficult 
to start :
13:17:37.965962 arp who-has djerba-gig tell canopus-gig
13:17:37.966220 IP djerba-gig > canopus-gig: udp
13:17:37.966230 IP djerba-gig > canopus-gig: udp
13:17:37.966313 IP djerba-gig > canopus-gig: udp
13:17:38.965906 arp who-has djerba-gig tell canopus-gig
13:17:38.966040 IP djerba-gig > canopus-gig: udp
This is strange since canopus is the one with Q6
  - ping does not start for a moment since all packets are RX-ERROR, then they 
start being received.

Here is the output of ethtool -S eth1

NIC statistics:
      rx_packets: 581
      tx_packets: 552
      rx_bytes: 545746
      tx_bytes: 66508
      rx_errors: 112950
      tx_errors: 0
      rx_dropped: 90
      tx_dropped: 0
      multicast: 0
      collisions: 0
      rx_length_errors: 0
      rx_over_errors: 0
      rx_crc_errors: 0
      rx_frame_errors: 0
      rx_fifo_errors: 112860
      rx_missed_errors: 112860
      tx_aborted_errors: 0
      tx_carrier_errors: 0
      tx_fifo_errors: 0
      tx_heartbeat_errors: 0
      tx_window_errors: 0
      tx_abort_late_coll: 0
      tx_deferred_ok: 0
      tx_single_coll_ok: 0
      tx_multi_coll_ok: 0
      rx_long_length_errors: 0
      rx_short_length_errors: 0
      rx_align_errors: 0
      tx_tcp_seg_good: 0
      tx_tcp_seg_failed: 0
      rx_flow_control_xon: 0
      rx_flow_control_xoff: 0
      tx_flow_control_xon: 45
      tx_flow_control_xoff: 112905
      rx_long_byte_count: 545746
      rx_csum_offload_good: 1
      rx_csum_offload_errors: 0


I rebooted with Q5 (+ netdev_max_backlog=32) and everything was fine. Is there 
anything I can do to make my report more useful for you ?

	

	P.O. Gaillard

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q6 - network is no longer smooth

[Ingo Molnar]

* P.O. Gaillard <pierre-olivier.gaillard@fr.thalesgroup.com> wrote:

> Hello,
> 
> I just tried with Q6 and the network behaviour seems odd :
>  - my ssh connection freezes a bit,
>  - communication between the two PCs sharing the GigE connection is 
>  difficult to start :

please try the -Q9 patch i just released, and if you still see any
problems does the following:

    echo 300 > /proc/sys/net/core/netdev_backlog_granularity

help?

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q9

[Thomas Charbonnel]

Ingo Molnar wrote :
> i've released the -Q9 patch:
> 
>   http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-Q9
> 
> ontop of:
> 
>   http://redhat.com/~mingo/voluntary-preempt/diff-bk-040828-2.6.8.1.bz2
> 
> Changes:
> 
>  - fixed the cond_resched_softirq() bug noticed by Mika Penttila.
> 
>  - updated the preemption-friendly network-RX code but 8193too.c still
>    produces delayed packets so netdev_backlog_granularity now defaults
>    to 2, which seems to be working fine on my testbox.

Thanks, network seems to be working fine with the new default value.
I still get > 140 us non-preemptible sections in rtl8139_pol, though :
http://www.undata.org/~thomas/q9_rtl8139.trace

Thomas

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q9

[Thomas Charbonnel]

Ingo Molnar wrote :
> i've released the -Q9 patch:
> 
>   http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-Q9

With ACPI compiled in and booting with acpi=off (which again doesn't
seem to be honoured), here's another weird one :

preemption latency trace v1.0.5 on 2.6.9-rc1-VP-Q9
--------------------------------------------------
 latency: 2888 us, entries: 37 (37)
    -----------------
    | task: swapper/0, uid:0 nice:0 policy:0 rt_prio:0
    -----------------
 => started at: do_IRQ+0x19/0x1a0
 => ended at:   do_IRQ+0x14d/0x1a0
=======>
00010000 0.000ms (+0.000ms): do_IRQ (common_interrupt)
00010000 0.000ms (+0.000ms): do_IRQ (default_idle)
00010000 0.000ms (+0.000ms): do_IRQ (<00000000>)
00010001 0.000ms (+0.002ms): mask_and_ack_8259A (do_IRQ)
00010001 0.002ms (+0.000ms): generic_redirect_hardirq (do_IRQ)
00010000 0.002ms (+0.000ms): generic_handle_IRQ_event (do_IRQ)
00010000 0.003ms (+0.000ms): timer_interrupt (generic_handle_IRQ_event)
00010001 0.003ms (+2.878ms): mark_offset_tsc (timer_interrupt)
00010001 2.882ms (+0.000ms): do_timer (timer_interrupt)
00010001 2.882ms (+0.000ms): update_process_times (do_timer)
00010001 2.882ms (+0.000ms): update_one_process (update_process_times)
00010001 2.882ms (+0.000ms): run_local_timers (update_process_times)
00010001 2.882ms (+0.000ms): raise_softirq (update_process_times)
00010001 2.882ms (+0.000ms): scheduler_tick (update_process_times)
00010001 2.883ms (+0.000ms): sched_clock (scheduler_tick)
00010001 2.883ms (+0.000ms): update_wall_time (do_timer)
00010001 2.883ms (+0.000ms): update_wall_time_one_tick
(update_wall_time)
00010001 2.883ms (+0.000ms): profile_tick (timer_interrupt)
00010001 2.884ms (+0.000ms): profile_hook (profile_tick)
00010002 2.884ms (+0.000ms): notifier_call_chain (profile_hook)
00010001 2.884ms (+0.000ms): profile_hit (timer_interrupt)
00010001 2.884ms (+0.000ms): generic_note_interrupt (do_IRQ)
00010001 2.884ms (+0.000ms): end_8259A_irq (do_IRQ)
00010001 2.885ms (+0.000ms): enable_8259A_irq (do_IRQ)
00000001 2.886ms (+0.000ms): do_softirq (do_IRQ)
00000001 2.886ms (+0.000ms): __do_softirq (do_softirq)
00000001 2.886ms (+0.000ms): wake_up_process (do_softirq)
00000001 2.886ms (+0.000ms): try_to_wake_up (wake_up_process)
00000001 2.886ms (+0.000ms): task_rq_lock (try_to_wake_up)
00000002 2.886ms (+0.000ms): activate_task (try_to_wake_up)
00000002 2.886ms (+0.000ms): sched_clock (activate_task)
00000002 2.887ms (+0.000ms): recalc_task_prio (activate_task)
00000002 2.887ms (+0.000ms): effective_prio (recalc_task_prio)
00000002 2.887ms (+0.000ms): enqueue_task (activate_task)
00000001 2.887ms (+0.000ms): preempt_schedule (try_to_wake_up)
00000001 2.888ms (+0.000ms): sub_preempt_count (do_IRQ)
00000001 2.888ms (+0.000ms): update_max_trace (check_preempt_timing)

Thomas

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q9

[Ingo Molnar]

* Thomas Charbonnel <thomas@undata.org> wrote:

> With ACPI compiled in and booting with acpi=off (which again doesn't
> seem to be honoured), here's another weird one :

> 00010000 0.003ms (+0.000ms): timer_interrupt (generic_handle_IRQ_event)
> 00010001 0.003ms (+2.878ms): mark_offset_tsc (timer_interrupt)
> 00010001 2.882ms (+0.000ms): do_timer (timer_interrupt)

do you have the NMI watchdog enabled? That could help us debugging this. 
Enabling the APIC/IO_APIC and using nmi_watchdog=1 would be the ideal
solution - if that doesnt work then nmi_watchdog=2 would be fine too,
but remove this code from arch/i386/kernel/nmi.c:

	if (nmi_watchdog == NMI_LOCAL_APIC)
		nmi_hz = 1;

(otherwise nmi_watchdog=2 would result in one NMI per second, not enough
to shed light on the above 2.8 msec latency.)

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q9

[Thomas Charbonnel]

Ingo Molnar wrote :

> do you have the NMI watchdog enabled? That could help us debugging this. 
> Enabling the APIC/IO_APIC and using nmi_watchdog=1 would be the ideal
> solution - if that doesnt work then nmi_watchdog=2 would be fine too,
> but remove this code from arch/i386/kernel/nmi.c:
> 
> 	if (nmi_watchdog == NMI_LOCAL_APIC)
> 		nmi_hz = 1;
> 
> (otherwise nmi_watchdog=2 would result in one NMI per second, not enough
> to shed light on the above 2.8 msec latency.)
> 
> 	Ingo

nmi_watchdog=1 worked fine.
Here's a trace (there seem to be a counter overflow) :

preemption latency trace v1.0.5 on 2.6.9-rc1-VP-Q9
--------------------------------------------------
 latency: 539 us, entries: 38 (38)
    -----------------
    | task: swapper/0, uid:0 nice:0 policy:0 rt_prio:0
    -----------------
 => started at: do_IRQ+0x19/0x190
 => ended at:   do_IRQ+0x14a/0x190
=======>
00010000 0.000ms (+0.000ms): do_IRQ (common_interrupt)
00010000 0.000ms (+0.000ms): do_IRQ (default_idle)
00010000 0.000ms (+0.000ms): do_IRQ (<00000000>)
00010001 0.000ms (+0.002ms): mask_and_ack_8259A (do_IRQ)
00010001 0.002ms (+0.000ms): generic_redirect_hardirq (do_IRQ)
00010000 0.002ms (+0.000ms): generic_handle_IRQ_event (do_IRQ)
00010000 0.002ms (+0.000ms): timer_interrupt (generic_handle_IRQ_event)
00010001 0.003ms (+0.005ms): mark_offset_tsc (timer_interrupt)
00010001 0.008ms (+0.000ms): do_timer (timer_interrupt)
00010001 0.008ms (+0.000ms): update_process_times (do_timer)
00010001 0.008ms (+0.000ms): update_one_process (update_process_times)
00010001 0.009ms (+0.000ms): run_local_timers (update_process_times)
00010001 0.009ms (+0.000ms): raise_softirq (update_process_times)
00010001 0.009ms (+0.000ms): scheduler_tick (update_process_times)
00010001 0.009ms (+0.000ms): sched_clock (scheduler_tick)
00010001 0.009ms (+0.000ms): update_wall_time (do_timer)
00010001 0.009ms (+0.000ms): update_wall_time_one_tick
(update_wall_time)
00010001 0.010ms (+0.000ms): generic_note_interrupt (do_IRQ)
00010001 0.010ms (+0.000ms): end_8259A_irq (do_IRQ)
00010001 0.010ms (+0.000ms): enable_8259A_irq (do_IRQ)
00000001 0.011ms (+0.524ms): do_softirq (do_IRQ)
00000001 0.535ms (+0.000ms): do_nmi (mcount)
00010001 0.536ms (+0.000ms): profile_tick (nmi_watchdog_tick)
00010001 0.536ms (+0.000ms): profile_hook (profile_tick)
00010002 0.536ms (+0.000ms): notifier_call_chain (profile_hook)
00010001 0.537ms (+689953.062ms): profile_hit (nmi_watchdog_tick)
00000002 689953.599ms (+1.523ms): sched_clock (activate_task)
00000001 0.537ms (+0.000ms): wake_up_process (do_softirq)
00000001 0.537ms (+0.000ms): try_to_wake_up (wake_up_process)
00000001 0.537ms (+0.000ms): task_rq_lock (try_to_wake_up)
00000002 0.537ms (+0.000ms): activate_task (try_to_wake_up)
00000002 0.538ms (+0.000ms): sched_clock (activate_task)
00000002 0.538ms (+0.000ms): recalc_task_prio (activate_task)
00000002 0.538ms (+0.000ms): effective_prio (recalc_task_prio)
00000002 0.538ms (+0.000ms): enqueue_task (activate_task)
00000001 0.538ms (+0.000ms): preempt_schedule (try_to_wake_up)
00000001 0.539ms (+0.000ms): sub_preempt_count (do_IRQ)
00000001 0.539ms (+0.000ms): update_max_trace (check_preempt_timing)

Thomas

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q6 - network is no longer smooth

[P.O. Gaillard]

Ingo Molnar wrote:> * P.O. Gaillard <pierre-olivier.gaillard@fr.thalesgroup.com> 
wrote:
> 
> 
>>Hello,
>>
>>I just tried with Q6 and the network behaviour seems odd :
>> - my ssh connection freezes a bit,
>> - communication between the two PCs sharing the GigE connection is 
>> difficult to start :
> 
> 
> please try the -Q9 patch i just released, and if you still see any
> problems does the following:
> 
>     echo 300 > /proc/sys/net/core/netdev_backlog_granularity
> 
> help?
>
Q9 just crashed after showing the login prompt. It says there is a kernel bug in 
netdevice.h at line 874

The backtrace is :
finegrained_poll
net_rx_action
___do_soft_irq
_do_soft_irq
ksoftirqd
kthread
ksoftirqd
kthread
kernel_thread_helper

I have the following modules :
e1000
i2c_isa
i2c_sensor
w83627hf
asus_acpi



	P.O. Gaillard

[patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Ingo Molnar]

i've released the -R0 patch:

  http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R0
 
ontop of:

  http://redhat.com/~mingo/voluntary-preempt/diff-bk-040828-2.6.8.1.bz2

i've given up on the netdev_backlog_granularity approach, and as a
replacement i've modified specific network drivers to return at a safe
point if softirq preemption is requested. This gives the same end result
but is more robust. For the time being i've fixed 8193too.c and e100.c.
(will fix up other drivers too as latencies get reported)

this should fix the crash reported by P.O. Gaillard, and it should solve
the packet delay/loss issues reported by Mark H Johnson. I cannot see
any problems on my rtl8193 testbox anymore.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Lee Revell]

On Thu, 2004-09-02 at 17:57, Ingo Molnar wrote:
> i've released the -R0 patch:
> 
>   http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R0
>  
> ontop of:
> 
>   http://redhat.com/~mingo/voluntary-preempt/diff-bk-040828-2.6.8.1.bz2
> 
> i've given up on the netdev_backlog_granularity approach, and as a
> replacement i've modified specific network drivers to return at a safe
> point if softirq preemption is requested.

Makes sense, netdev_max_backlog never made a difference on my system
(via-rhine driver).

If you read that Microsoft paper I posted a link to earlier, they
describe all of the main categories of latencies we have dealt with. 
They give special mention to network driver DPCs/softirqs.

The worst offender was a driver that used a DPC/softirq to reset the
card if there was no traffic in 10 seconds, to work around a hardware
lockup bug in some versions.  Since the reset path was never designed to
be fast this caused problems.  They also mention a similar problem to
the one that still exists with the via-rhine driver (fixed in -mm) where
it uses a DPC to poll for link status.

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Ingo Molnar]

* Lee Revell <rlrevell@joe-job.com> wrote:

> > i've given up on the netdev_backlog_granularity approach, and as a
> > replacement i've modified specific network drivers to return at a safe
> > point if softirq preemption is requested.
> 
> Makes sense, netdev_max_backlog never made a difference on my system
> (via-rhine driver).

via-rhine does RX processing from the hardirq handler, this codepath is
harder to break up. The NAPI ->poll functions used by e100 and 8193too
are much easier to break up because RX throttling and re-trying is a
basic property of NAPI.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Lee Revell]

On Thu, 2004-09-02 at 18:14, Ingo Molnar wrote:
> * Lee Revell <rlrevell@joe-job.com> wrote:
> 
> > > i've given up on the netdev_backlog_granularity approach, and as a
> > > replacement i've modified specific network drivers to return at a safe
> > > point if softirq preemption is requested.
> > 
> > Makes sense, netdev_max_backlog never made a difference on my system
> > (via-rhine driver).
> 
> via-rhine does RX processing from the hardirq handler, this codepath is
> harder to break up. The NAPI ->poll functions used by e100 and 8193too
> are much easier to break up because RX throttling and re-trying is a
> basic property of NAPI.
> 

What I meant was, I did not consider the latencies from via-rhine to be
a problem.  The other posters reported 300-500 usec latencies in the
network driver, I did not see this.

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Lee Revell]

On Thu, 2004-09-02 at 03:15, Ingo Molnar wrote:
> * Lee Revell <rlrevell@joe-job.com> wrote:
> 
> > Here are traces of a 145, 190, and 217 usec latencies in
> > netif_receive_skb:
> > 
> > http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace2.txt
> > http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace3.txt
> > http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/trace4.txt
> 
> these all seem to be single-packet processing latencies - it would be
> quite hard to make those codepaths preemptible.
> 
> i'd suggest to turn off things like netfilter and ip_conntrack (and
> other optional networking features that show up in the trace), they can
> only increase latency:
> 

Do you see any optional networking features in the trace (other than
ip_conntrack)?  I was under the impression that I had everything
optional disabled.

Lee  

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Ingo Molnar]

* Lee Revell <rlrevell@joe-job.com> wrote:

> Do you see any optional networking features in the trace (other than
> ip_conntrack)?  I was under the impression that I had everything
> optional disabled.

yeah, it seems to be only ip_conntrack and netfilter (which conntrack
relies on).

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Lee Revell]

On Thu, 2004-09-02 at 19:28, Ingo Molnar wrote:
> * Lee Revell <rlrevell@joe-job.com> wrote:
> 
> > Do you see any optional networking features in the trace (other than
> > ip_conntrack)?  I was under the impression that I had everything
> > optional disabled.
> 
> yeah, it seems to be only ip_conntrack and netfilter (which conntrack
> relies on).
> 

FWIW these seem to only slow down the single packet path by about 10%. 
This is pretty good.

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Lee Revell]

On Thu, 2004-09-02 at 18:14, Ingo Molnar wrote:
> * Lee Revell <rlrevell@joe-job.com> wrote:
> 
> > > i've given up on the netdev_backlog_granularity approach, and as a
> > > replacement i've modified specific network drivers to return at a safe
> > > point if softirq preemption is requested.
> > 
> > Makes sense, netdev_max_backlog never made a difference on my system
> > (via-rhine driver).
> 
> via-rhine does RX processing from the hardirq handler, this codepath is
> harder to break up. The NAPI ->poll functions used by e100 and 8193too
> are much easier to break up because RX throttling and re-trying is a
> basic property of NAPI.
> 

Judging from these graphs, all of the latency issues are solved, at
least on my UP hardware, and the latencies seem to be getting very close
to the limits of what the hardware can do:

http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/jack-test-1

The worst case latency is only 160 usecs, and the vast majority fall
into the pattern from 0 to 120 usecs.  All of the spikes above 120 are
almost certainly caused by netdev_max_backlog.  However these are not
long enough to cause any problems with my workload; the lowest practical
latency for audio work is around 0.66 ms (32 frames at 48khz). 

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q8

[Rusty Russell]

On Thu, 2004-09-02 at 17:46, Ingo Molnar wrote:
> Rusty, what's going on in this code?

Good question!  Not my code, fortunately...

> #1: we kmalloc(GFP_KERNEL) with a spinlock held and softirqs off - ouch!
> 
> #2: why does it do the kmalloc() anyway? It could store the position in
>     the seq pointer just fine. No need to alloc an integer pointer to
>     store the value in ...
> 
> #3: to fix the latency, ct_seq_show() could take the ip_conntrack_lock 
>     and could check the current index against ip_conntrack_htable_size. 
>     There's not much point in making this non-preemptible, there's 
>     a 4K granularity anyway.

The code tries to put an entire hash bucket into a single seq_read(). 
That's not going to work if the hash is really deep.  On the other hand,
not much will, and it's simple.

The lock is only needed on traversing: htable_size can't change after
init anyway, so it should be done in ct_seq_show.

Fix should be fairly simple...
Rusty.
-- 
Anyone who quotes me in their signature is an idiot -- Rusty Russell

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Eric St-Laurent]

> Judging from these graphs, all of the latency issues are solved, at
> least on my UP hardware, and the latencies seem to be getting very close
> to the limits of what the hardware can do:
> 
> http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/jack-test-1
> 
> The worst case latency is only 160 usecs, and the vast majority fall
> into the pattern from 0 to 120 usecs.  All of the spikes above 120 are
> almost certainly caused by netdev_max_backlog.  However these are not
> long enough to cause any problems with my workload; the lowest practical
> latency for audio work is around 0.66 ms (32 frames at 48khz). 

Lee,

A few weeks ago you wrote that "the worst latency I was able to trigger
was 46 usecs", now it's 160 usecs.

Ingo has done much work on his patches since then.

Why the worst latency is higher now? I presume that the latency
measurements technique are more accurate and the 46 usecs was
inaccurate?

Ref: http://uwsg.indiana.edu/hypermail/linux/kernel/0407.3/0994.html

Best regards,

Eric St-Laurent

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Lee Revell]

On Thu, 2004-09-02 at 23:17, Eric St-Laurent wrote:
> > Judging from these graphs, all of the latency issues are solved, at
> > least on my UP hardware, and the latencies seem to be getting very close
> > to the limits of what the hardware can do:
> > 
> > http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6#/var/www/2.6.9-rc1-Q6/jack-test-1
> > 
> > The worst case latency is only 160 usecs, and the vast majority fall
> > into the pattern from 0 to 120 usecs.  All of the spikes above 120 are
> > almost certainly caused by netdev_max_backlog.  However these are not
> > long enough to cause any problems with my workload; the lowest practical
> > latency for audio work is around 0.66 ms (32 frames at 48khz). 
> 
> Lee,
> 
> A few weeks ago you wrote that "the worst latency I was able to trigger
> was 46 usecs", now it's 160 usecs.
> 
> Ingo has done much work on his patches since then.
> 
> Why the worst latency is higher now? I presume that the latency
> measurements technique are more accurate and the 46 usecs was
> inaccurate?
> 
> Ref: http://uwsg.indiana.edu/hypermail/linux/kernel/0407.3/0994.html
> 

Yup, due to my incomplete understanding of the jackd code, my initial
measurements were measuring the time it took to run one process cycle
(basically a NOOP if there are no clients), rather than the actual time
jackd spent in poll() between cycles.

This did have the effect of measuring the scueduler latency, but I
believe it was being measured indirectly via cache effects - the longer
it had been since jackd last ran, the colder the cachelines touched by
the last cycle.

Since I am using a patch to jackd to measure these latencies, which will
be merged in the near future, it's more important for me that the patch
accurately reflect the latencies jackd users will see than it is for the
new, accurate results to be compatible with the old.

All datasets for -O and earlier use the old code:

	http://krustophenia.net/testresults.php?dataset=2.6.8-rc3-O5

This one uses the initial version of the new code, measuring the time
jackd spends in poll().  The bimodal distribution is due to my sound
card having two different interrupt sources for capture and playback. 
So one of the spikes represent the elapsed time between the capture
interrupt and the playback interrupt, and the other the time between the
playback interrupt and the next capture interrupt:
	
	http://krustophenia.net/testresults.php?dataset=2.6.8.1-P0


-Q and later use the current method, which is like the above except the
second hump is discarded, as it is a function of the scheduling latency
and the period size rather than just the scheduling latency:

	http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6

So, don't be fooled by the numbers, the newest version of the patch is
in fact the best.  I have been meaning to go back and measure the
current patches with the old code but it's pretty low priority...

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Ingo Molnar]

* Lee Revell <rlrevell@joe-job.com> wrote:

> -Q and later use the current method, which is like the above except
> the second hump is discarded, as it is a function of the scheduling
> latency and the period size rather than just the scheduling latency:
> 
> 	http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6
> 
> So, don't be fooled by the numbers, the newest version of the patch is
> in fact the best.  I have been meaning to go back and measure the
> current patches with the old code but it's pretty low priority...

vanilla kernel 2.6.8.1 would be quite interesting to get a few charts of
- especially if your measurement methodology has changed. There's not
much sense in re-testing older VP patches.

also, has the userspace workload you are using stayed constant during
all these tests?

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Lee Revell]

On Fri, 2004-09-03 at 02:36, Ingo Molnar wrote:
> * Lee Revell <rlrevell@joe-job.com> wrote:
> 
> > -Q and later use the current method, which is like the above except
> > the second hump is discarded, as it is a function of the scheduling
> > latency and the period size rather than just the scheduling latency:
> > 
> > 	http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q6
> > 
> > So, don't be fooled by the numbers, the newest version of the patch is
> > in fact the best.  I have been meaning to go back and measure the
> > current patches with the old code but it's pretty low priority...
> 
> vanilla kernel 2.6.8.1 would be quite interesting to get a few charts of
> - especially if your measurement methodology has changed.

OK, I will give this a shot.  Now that the VP patches are stabilizing I
will be doing more profiling.  I also want to try the -mm kernel, this
has some interesting differences from the stock kernel.  For example I
measured about a 10% improvement with the old method, which implies a
big performance gain.

>  There's not
> much sense in re-testing older VP patches.
> 

Yup, my thoughts exactly, this would just tell us what we already know,
that the latency gets better with each version.

> also, has the userspace workload you are using stayed constant during
> all these tests?
> 

I am mostly just using normal desktop hacker workloads, web browsing,
email, builds.  Lately I am using the box as a Samba server.  At first,
I was stressing the system using every disk benchmark I could think of,
but it never seemed to affect the worst case and did not even change the
shape of the distribution much, so I don't bother.  For all practical
purposes, it's impossible to change the shape of these graphs much by
stressing the system.

I am able to induce large latencies by using up all available swap with
make -j12 on a KDE program, and by pingflooding the broadcast address,
but these are pathological enough that I have not worried about them.

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Ingo Molnar]

* Lee Revell <rlrevell@joe-job.com> wrote:

> > vanilla kernel 2.6.8.1 would be quite interesting to get a few charts of
> > - especially if your measurement methodology has changed.
> 
> OK, I will give this a shot.  Now that the VP patches are stabilizing
> I will be doing more profiling.  I also want to try the -mm kernel,
> this has some interesting differences from the stock kernel.  For
> example I measured about a 10% improvement with the old method, which
> implies a big performance gain.

the -mm kernel used to have additional *-latency-fix patches that were
done based on the initial preemption-timing patch in -mm and partly
based on early VP discussions and findings. I recently reviewed and
merged the 2-3 missing ones into VP. Andrew has dropped these patches
meanwhile and i expect to submit the cleaner and more complete solution
that is in VP.

So i'd expect -mm to still perform better than vanilla (it usually
does), but if that big 10% difference in latencies doesnt show up
anymore i'd attribute it to the shuffling around of latency related
patches, not some genuine deficiency in -mm.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Ingo Molnar]

another question - any objections against me rebasing the VP patch to
the current -mm tree and keeping it there exclusively until all possible
merges are done? It would probably quite some work to create a complete
patch for the upstream or BK tree during that process, as small patches
start to flow in the VP => -mm => BK direction. Would any of the regular
VP users/testers be wary to use the -mm tree?

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Lee Revell]

On Fri, 2004-09-03 at 03:05, Ingo Molnar wrote:
> another question - any objections against me rebasing the VP patch to
> the current -mm tree and keeping it there exclusively until all possible
> merges are done? It would probably quite some work to create a complete
> patch for the upstream or BK tree during that process, as small patches
> start to flow in the VP => -mm => BK direction. Would any of the regular
> VP users/testers be wary to use the -mm tree?
> 

None here.  Assuming the SMP issues are resolved, then the only
remaining issues on UP will probably be with various drivers, those
fixes should apply just as easily to -mm as vanilla.

As far as I am concerned the VP patches are stable enough for the
audio-centric distros to start distributing VP kernel packages, these
will certainly be using the vanilla kernel.  I think the PlanetCCRMA and
AGNULA people are planning to start distributing test VP-kernel packages
as soon as the patches stabilize.  IIRC Nando is on vacation this week.

I will make an announcement on LAD that as of R0 the VP patches should
be stable and are ready for wider testing.  You may want to wait until
after the initial slew of bug reports before rebasing VP against MM.  I
suspect most of the problems with be driver specific, and most of the
fixes will apply equally to -mm and vanilla.

I have added Luke (AudioSlack), Free (AGNULA), and Nando (CCRMA) to the
cc: list.  They would be in the best position to answer your question.

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Free Ekanayaka]

|--==> "LR" == Lee Revell <rlrevell@joe-job.com> writes:

  LR> On Fri, 2004-09-03 at 03:05, Ingo Molnar wrote:
  >>another question - any objections against me rebasing the VP patch to
  >>the current -mm tree and keeping it there exclusively until all possible
  >>merges are done? It would probably quite some work to create a complete
  >>patch for the upstream or BK tree during that process, as small patches
  >>start to flow in the VP => -mm => BK direction. Would any of the regular
  >>VP users/testers be wary to use the -mm tree?
  >>

  LR> None here.  Assuming the SMP issues are resolved, then the only
  LR> remaining issues on UP will probably be with various drivers, those
  LR> fixes should apply just as easily to -mm as vanilla.

  LR> As far as I am concerned the VP patches are stable enough for the
  LR> audio-centric distros to start distributing VP kernel packages, these
  LR> will certainly be using the vanilla kernel.  I think the PlanetCCRMA and
  LR> AGNULA people are planning to start distributing test VP-kernel packages
  LR> as soon as the patches stabilize.  IIRC Nando is on vacation this week.

  LR> I will make an announcement on LAD that as of R0 the VP patches should
  LR> be stable and are ready for wider testing.  You may want to wait until
  LR> after the initial slew of bug reports before rebasing VP against MM.  I
  LR> suspect most of the problems with be driver specific, and most of the
  LR> fixes will apply equally to -mm and vanilla.

  LR> I have added Luke (AudioSlack), Free (AGNULA), and Nando (CCRMA) to the
  LR> cc: list.  They would be in the best position to answer your question.

Yes, you're right. We plan to  provide test 2.6.x  packages as soon as
patches stabilise. Please let me  know if you have some recommendation
(configuration flags, additional patches, etc.).

Cheers,

Free

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Lee Revell]

On Fri, 2004-09-03 at 03:50, Free Ekanayaka wrote:
>   LR> As far as I am concerned the VP patches are stable enough for the
>   LR> audio-centric distros to start distributing VP kernel packages, these
>   LR> will certainly be using the vanilla kernel.  I think the PlanetCCRMA and
>   LR> AGNULA people are planning to start distributing test VP-kernel packages
>   LR> as soon as the patches stabilize.  IIRC Nando is on vacation this week.
> 
>   LR> I will make an announcement on LAD that as of R0 the VP patches should
>   LR> be stable and are ready for wider testing.  You may want to wait until
>   LR> after the initial slew of bug reports before rebasing VP against MM.  I
>   LR> suspect most of the problems with be driver specific, and most of the
>   LR> fixes will apply equally to -mm and vanilla.
> 
>   LR> I have added Luke (AudioSlack), Free (AGNULA), and Nando (CCRMA) to the
>   LR> cc: list.  They would be in the best position to answer your question.
> 
> Yes, you're right. We plan to  provide test 2.6.x  packages as soon as
> patches stabilise. Please let me  know if you have some recommendation
> (configuration flags, additional patches, etc.).
> 

As of -R0 it's definitely stable on UP and SMP users are reporting the
same.  All known problems should be fixed, and there are no known
regressions.  You should probably post a UP version and have your users
test that before posting SMP packages, the latter are not quite as well
tested.

No other patches (ie various scheduler tweaks, CK) should be necessary,
and in fact are not recommended because they might mask latency issues
that we would rather fix.

I use Debian unstable which should be pretty close to AGNULA, and for
several weeks now I have been unable to produce an xrun in jack at 32
frames no matter what I throw at the machine.  I actually have not had
xrun debugging enabled in weeks because I don't get any xruns.

Any problems at this point are most likely going to involve less common
hardware, stuff the LKML testers don't have.

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Luke Yelavich]

On Fri, Sep 03, 2004 at 05:40:34PM EST, Lee Revell wrote:
> On Fri, 2004-09-03 at 03:05, Ingo Molnar wrote:
> > another question - any objections against me rebasing the VP patch to
> > the current -mm tree and keeping it there exclusively until all possible
> > merges are done? It would probably quite some work to create a complete
> > patch for the upstream or BK tree during that process, as small patches
> > start to flow in the VP => -mm => BK direction. Would any of the regular
> > VP users/testers be wary to use the -mm tree?
> > 
> 
> None here.  Assuming the SMP issues are resolved, then the only
> remaining issues on UP will probably be with various drivers, those
> fixes should apply just as easily to -mm as vanilla.
> 
> As far as I am concerned the VP patches are stable enough for the
> audio-centric distros to start distributing VP kernel packages, these
> will certainly be using the vanilla kernel.  I think the PlanetCCRMA and
> AGNULA people are planning to start distributing test VP-kernel packages
> as soon as the patches stabilize.  IIRC Nando is on vacation this week.

I certainly have intensions of making test kernels available in my repository
in a separate testing branch. I don't really mind for myself what tree the
patch is based on, but I feel that the patches may get more testing if they
are against vanilla, rather than against another tree, as users 
may consider the patch to be more stable. On the other hand, it is not hard for
packagers like myself to do the leg work, and we can also provide a pre-patched
kernel source for those who still want to roll their own.

> I will make an announcement on LAD that as of R0 the VP patches should
> be stable and are ready for wider testing.  You may want to wait until
> after the initial slew of bug reports before rebasing VP against MM.  I
> suspect most of the problems with be driver specific, and most of the
> fixes will apply equally to -mm and vanilla.

Well with Lee's help, I think I have identified an ICE1712 sound driver issue,
but this is yet to be determined.

> I have added Luke (AudioSlack), Free (AGNULA), and Nando (CCRMA) to the
> cc: list.  They would be in the best position to answer your question.

I will go with whatever is decided, as I am prepared to do the legwork for my
repository users.
-- 
Luke Yelavich
http://www.audioslack.com
luke@audioslack.com

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Lee Revell]

On Fri, 2004-09-03 at 04:09, Luke Yelavich wrote:
> On Fri, Sep 03, 2004 at 05:40:34PM EST, Lee Revell wrote:
> > On Fri, 2004-09-03 at 03:05, Ingo Molnar wrote:
> Well with Lee's help, I think I have identified an ICE1712 sound driver issue,
> but this is yet to be determined.

Hmm, this one is still not fixed, using the latest VP patches?

What are the symptoms again?

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Luke Yelavich]

On Fri, Sep 03, 2004 at 06:13:16PM EST, Lee Revell wrote:
> > On Fri, Sep 03, 2004 at 05:40:34PM EST, Lee Revell wrote:
> > > On Fri, 2004-09-03 at 03:05, Ingo Molnar wrote:
> > Well with Lee's help, I think I have identified an ICE1712 sound driver issue,
> > but this is yet to be determined.
> 
> Hmm, this one is still not fixed, using the latest VP patches?

I have been keeping up with the patches, but haven't had a chance to try it out
with them lately. Currently building the latest one, and will be able to test
again when done.
-- 
Luke Yelavich
http://www.audioslack.com
luke@audioslack.com

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Free Ekanayaka]

|--==> "LR" == Lee Revell <rlrevell@joe-job.com> writes:

  LR> On Fri, 2004-09-03 at 03:50, Free Ekanayaka wrote:
  LR> As far as I am concerned the VP patches are stable enough for the
  LR> audio-centric distros to start distributing VP kernel packages, these
  LR> will certainly be using the vanilla kernel.  I think the PlanetCCRMA and
  LR> AGNULA people are planning to start distributing test VP-kernel packages
  LR> as soon as the patches stabilize.  IIRC Nando is on vacation this week.
  >>
  LR> I will make an announcement on LAD that as of R0 the VP patches should
  LR> be stable and are ready for wider testing.  You may want to wait until
  LR> after the initial slew of bug reports before rebasing VP against MM.  I
  LR> suspect most of the problems with be driver specific, and most of the
  LR> fixes will apply equally to -mm and vanilla.
  >>
  LR> I have added Luke (AudioSlack), Free (AGNULA), and Nando (CCRMA) to the
  LR> cc: list.  They would be in the best position to answer your question.
  >>
  >>Yes, you're right. We plan to  provide test 2.6.x  packages as soon as
  >>patches stabilise. Please let me  know if you have some recommendation
  >>(configuration flags, additional patches, etc.).
  >>

  LR> As of -R0 it's definitely stable on UP and SMP users are reporting the
  LR> same.  All known problems should be fixed, and there are no known
  LR> regressions.  You should probably post a UP version and have your users
  LR> test that before posting SMP packages, the latter are not quite as well
  LR> tested.

  LR> No other patches (ie various scheduler tweaks, CK) should be necessary,
  LR> and in fact are not recommended because they might mask latency issues
  LR> that we would rather fix.

  LR> I use Debian unstable which should be pretty close to AGNULA, and for
  LR> several weeks now I have been unable to produce an xrun in jack at 32
  LR> frames no matter what I throw at the machine.  I actually have not had
  LR> xrun debugging enabled in weeks because I don't get any xruns.

  LR> Any problems at this point are most likely going to involve less common
  LR> hardware, stuff the LKML testers don't have.

A/DeMuDi is based on  a sarge  snapshot (currently  17 July.. time  to
shift  forward!), plus some bits of  sid  (especially up to date audio
packages).

Which kernel tree are you using?

Have you built your kernel starting from the stock kernel-source-2.6.8
package along with the relevant debian patch?

Cheers,

Free

[patch] voluntary-preempt-2.6.9-rc1-bk4-R1

[Ingo Molnar]

* Lee Revell <rlrevell@joe-job.com> wrote:

> As of -R0 it's definitely stable on UP and SMP users are reporting the
> same.  All known problems should be fixed, and there are no known
> regressions.  You should probably post a UP version and have your
> users test that before posting SMP packages, the latter are not quite
> as well tested.

Florian Schmidt reported a minor bug that prevents a successful build if
!CONFIG_LATENCY_TRACE - i've uploaded -R1 that fixes this:
  
 http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R1

there are no other changes in -R1, and there are no known pending bugs
currently.

for a packaged kernel i'd suggest to enable all the CONFIG_PREEMPT_*
values in the .config, including CONFIG_PREEMPT_TIMING.

CONFIG_LATENCY_TRACE can add overhead if active, so while it would be
useful for initial packages to enable this .config option, i'd suggest
to turn it off by default by changing 'tracing_enabled = 1' to
'tracing_enabled = 0' in the patch. Then people can enable it and do
precise tracing whenever they encounter a particular high latency on
their system.

configuring the threaded/nonthreaded properties of IRQ handlers can be
tricky. Perhaps a script could scan /proc (and/or /sys) for audio
interrupts and make them directly executed? Unfortunately audio
interrupt handler requests dont seem to be going through some central
ALSA function so i see no easy way to somehow tag audio interrupts
automatically and provide some /proc flag to make audio interrupts
non-threaded by default.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R1

[Luke Yelavich]

On Fri, Sep 03, 2004 at 07:25:47PM EST, Ingo Molnar wrote:
> 
> * Lee Revell <rlrevell@joe-job.com> wrote:
> 
> > As of -R0 it's definitely stable on UP and SMP users are reporting the
> > same.  All known problems should be fixed, and there are no known
> > regressions.  You should probably post a UP version and have your
> > users test that before posting SMP packages, the latter are not quite
> > as well tested.
> 
> Florian Schmidt reported a minor bug that prevents a successful build if
> !CONFIG_LATENCY_TRACE - i've uploaded -R1 that fixes this:
>   
>  http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R1
> 
> there are no other changes in -R1, and there are no known pending bugs
> currently.

I think I might be having a problem here, that I didn't have with previous
patches. Bare in mind that the previous patch I tested was against 2.6.8.1
vanilla.

I am using a D-Link KVM here between my notebook and my desktop machine.
It is the desktop I am currently testing these patches on, and the KVM
requires a double-tap of the scroll lock key to switch between machines. With
the latest R0 patch, something is not working when I attempt to change from
my desktop to my notebook. The KVM usually lets out a beep when I can
use the arrow keys to switch, but it isn't here. Adding to that, my console
locks up totally for about 10 seconds, before allowing me to go on and
type commands. I also seem to get some debugging output or a trace of
some sort when rebooting, and the kernel panics with the message:
(0)Kernel Panic - not syncing: Failed exception in interrupt

Included is some dmesg output from beginning of bootup.

Let me know if any more info is needed.
-- 
Luke Yelavich
http://www.audioslack.com
luke@audioslack.com

CPU: After generic identify, caps: bfebfbff 00000000 00000000 00000000
CPU: After vendor identify, caps:  bfebfbff 00000000 00000000 00000000
CPU: Trace cache: 12K uops, L1 D cache: 8K
CPU: L2 cache: 512K
CPU: After all inits, caps:        bfebfbff 00000000 00000000 00000080
CPU: Intel(R) Pentium(R) 4 CPU 2.40GHz stepping 07
Enabling fast FPU save and restore... done.
Enabling unmasked SIMD FPU exception support... done.
Checking 'hlt' instruction... OK.
Badness in schedule at kernel/sched.c:2637
 [<c0302fb0>] schedule+0x558/0x55d
 [<c0302ff5>] preempt_schedule+0x40/0x5f
 [<c010041f>] rest_init+0x67/0x73
 [<c03da780>] start_kernel+0x195/0x1d4
 [<c03da38c>] unknown_bootoption+0x0/0x147
(swapper/1): new 666 us maximum-latency critical section.
 => started at: <preempt_schedule+0x3b/0x5f>
 => ended at:   <finish_task_switch+0x37/0x93>
 [<c012f01f>] check_preempt_timing+0x11b/0x1da
 [<c01103df>] finish_task_switch+0x37/0x93
 [<c01103df>] finish_task_switch+0x37/0x93
 [<c012f212>] sub_preempt_count+0x4d/0x65
 [<c012f212>] sub_preempt_count+0x4d/0x65
 [<c01103df>] finish_task_switch+0x37/0x93
 [<c011045e>] schedule_tail+0x23/0x5c
 [<c0105f5e>] ret_from_fork+0x6/0x14
 [<c010046b>] init+0x0/0x179
 [<c0104210>] kernel_thread_helper+0x0/0xb
Badness in schedule at kernel/sched.c:2637
 [<c0302fb0>] schedule+0x558/0x55d
 [<c0302ff5>] preempt_schedule+0x40/0x5f
 [<c0110439>] finish_task_switch+0x91/0x93
 [<c011045e>] schedule_tail+0x23/0x5c
 [<c0105f5e>] ret_from_fork+0x6/0x14
 [<c010046b>] init+0x0/0x179
 [<c0104210>] kernel_thread_helper+0x0/0xb
NET: Registered protocol family 16
PCI: PCI BIOS revision 2.10 entry at 0xf1e60, last bus=2
(swapper/1): new 904 us maximum-latency critical section.
 => started at: <cond_resched+0xd/0x41>
 => ended at:   <cond_resched+0xd/0x41>
 [<c012f01f>] check_preempt_timing+0x11b/0x1da
 [<c0303417>] cond_resched+0xd/0x41
 [<c0303417>] cond_resched+0xd/0x41
 [<c012f114>] touch_preempt_timing+0x36/0x3a
 [<c012f114>] touch_preempt_timing+0x36/0x3a
 [<c0303417>] cond_resched+0xd/0x41
 [<c0138b6b>] kmem_cache_alloc+0x5f/0x61
 [<c0119fe8>] __request_region+0x26/0xbd
 [<c03f1336>] pci_direct_init+0x3e/0x10e
 [<c03da807>] do_initcalls+0x2f/0xbc
 [<c01004c4>] init+0x59/0x179
 [<c010046b>] init+0x0/0x179
 [<c0104215>] kernel_thread_helper+0x5/0xb
PCI: Using configuration type 1
Linux Plug and Play Support v0.97 (c) Adam Belay
SCSI subsystem initialized
usbcore: registered new driver usbfs
usbcore: registered new driver hub

<snip>

get_random_bytes called before random driver initialization
(swapper/1): new 6605 us maximum-latency critical section.
 => started at: <cond_resched+0xd/0x41>
 => ended at:   <cond_resched+0xd/0x41>
 [<c012f01f>] check_preempt_timing+0x11b/0x1da
 [<c0303417>] cond_resched+0xd/0x41
 [<c0303417>] cond_resched+0xd/0x41
 [<c012f114>] touch_preempt_timing+0x36/0x3a
 [<c012f114>] touch_preempt_timing+0x36/0x3a
 [<c0303417>] cond_resched+0xd/0x41
 [<c0138da7>] __kmalloc+0x89/0x90
 [<c0183f6c>] proc_create+0x86/0xd9
 [<c018416b>] create_proc_entry+0x66/0xc9
 [<c03f1fcc>] dev_proc_init+0x2b/0xa3
 [<c03f206c>] net_dev_init+0x28/0x17c
 [<c03f1ce4>] pcibios_init+0x65/0x7e
 [<c03da807>] do_initcalls+0x2f/0xbc
 [<c01004c4>] init+0x59/0x179
 [<c010046b>] init+0x0/0x179
 [<c0104215>] kernel_thread_helper+0x5/0xb
(swapper/1): new 43385 us maximum-latency critical section.
 => started at: <cond_resched+0xd/0x41>
 => ended at:   <cond_resched+0xd/0x41>
 [<c012f01f>] check_preempt_timing+0x11b/0x1da
 [<c0303417>] cond_resched+0xd/0x41
 [<c0107b1d>] do_IRQ+0x14a/0x18e
 [<c0303417>] cond_resched+0xd/0x41
 [<c012f114>] touch_preempt_timing+0x36/0x3a
 [<c012f114>] touch_preempt_timing+0x36/0x3a
 [<c0303417>] cond_resched+0xd/0x41
 [<c0138b6b>] kmem_cache_alloc+0x5f/0x61
 [<c0119fe8>] __request_region+0x26/0xbd
 [<c01efb09>] isapnp_next_rdp+0x66/0xa1
 [<c03e6d2d>] isapnp_isolate_rdp_select+0x5b/0xc5
 [<c03e6eda>] isapnp_isolate+0x143/0x1f8
 [<c03e7c15>] isapnp_init+0xbb/0x2da
 [<c03da807>] do_initcalls+0x2f/0xbc
 [<c01004c4>] init+0x59/0x179
 [<c010046b>] init+0x0/0x179
 [<c0104215>] kernel_thread_helper+0x5/0xb
(swapper/1): new 43492 us maximum-latency critical section.
 => started at: <cond_resched+0xd/0x41>
 => ended at:   <cond_resched+0xd/0x41>
 [<c012f01f>] check_preempt_timing+0x11b/0x1da
 [<c0303417>] cond_resched+0xd/0x41
 [<c0303417>] cond_resched+0xd/0x41
 [<c012f114>] touch_preempt_timing+0x36/0x3a
 [<c012f114>] touch_preempt_timing+0x36/0x3a
 [<c0303417>] cond_resched+0xd/0x41
 [<c0138b6b>] kmem_cache_alloc+0x5f/0x61
 [<c0119fe8>] __request_region+0x26/0xbd
 [<c01efb09>] isapnp_next_rdp+0x66/0xa1
 [<c03e6d2d>] isapnp_isolate_rdp_select+0x5b/0xc5
 [<c03e6eda>] isapnp_isolate+0x143/0x1f8
 [<c03e7c15>] isapnp_init+0xbb/0x2da
 [<c03da807>] do_initcalls+0x2f/0xbc
 [<c01004c4>] init+0x59/0x179
 [<c010046b>] init+0x0/0x179
 [<c0104215>] kernel_thread_helper+0x5/0xb
(swapper/1): new 43561 us maximum-latency critical section.
 => started at: <cond_resched+0xd/0x41>
 => ended at:   <cond_resched+0xd/0x41>
 [<c012f01f>] check_preempt_timing+0x11b/0x1da
 [<c0303417>] cond_resched+0xd/0x41
 [<c0107b1d>] do_IRQ+0x14a/0x18e
 [<c0303417>] cond_resched+0xd/0x41
 [<c012f114>] touch_preempt_timing+0x36/0x3a
 [<c012f114>] touch_preempt_timing+0x36/0x3a
 [<c0303417>] cond_resched+0xd/0x41
 [<c0138b6b>] kmem_cache_alloc+0x5f/0x61
 [<c0119fe8>] __request_region+0x26/0xbd
 [<c01efb09>] isapnp_next_rdp+0x66/0xa1
 [<c03e6d2d>] isapnp_isolate_rdp_select+0x5b/0xc5
 [<c03e6eda>] isapnp_isolate+0x143/0x1f8
 [<c03e7c15>] isapnp_init+0xbb/0x2da
 [<c03da807>] do_initcalls+0x2f/0xbc
 [<c01004c4>] init+0x59/0x179
 [<c010046b>] init+0x0/0x179
 [<c0104215>] kernel_thread_helper+0x5/0xb
isapnp: No Plug & Play device found
requesting new irq thread for IRQ8...
Real Time Clock Driver v1.12
Using anticipatory io scheduler
<snip>
requesting new irq thread for IRQ6...
<snip>
IRQ#6 thread started up.
eth0: Tigon3 [partno(BCM95702A20) rev 1002 PHY(5703)] (PCI:33MHz:32-bit) 10/100/1000BaseT Ethernet 00:e0:18:df:d5:b6
eth0: HostTXDS[1] RXcsums[1] LinkChgREG[0] MIirq[0] ASF[0] Split[0] WireSpeed[1] TSOcap[1] 
requesting new irq thread for IRQ3...
(dhcpcd/2226): new 115753 us maximum-latency critical section.
 => started at: <tg3_open+0xc9/0x263 [tg3]>
 => ended at:   <tg3_open+0x122/0x263 [tg3]>
 [<c012f01f>] check_preempt_timing+0x11b/0x1da
 [<f88c805a>] tg3_open+0x122/0x263 [tg3]
 [<f88c805a>] tg3_open+0x122/0x263 [tg3]
 [<c012f212>] sub_preempt_count+0x4d/0x65
 [<c012f212>] sub_preempt_count+0x4d/0x65
 [<f88c805a>] tg3_open+0x122/0x263 [tg3]
 [<c029f2ad>] dev_open+0xcf/0xfe
 [<c02a30c1>] dev_mc_upload+0x3d/0x5d
 [<c02a0987>] dev_change_flags+0x5b/0x12c
 [<c029e930>] __dev_get_by_name+0xe/0xb9
 [<c02e2d4b>] devinet_ioctl+0x247/0x5c1
 [<c02e5066>] inet_ioctl+0x5f/0x9f
 [<c0301f9d>] packet_ioctl+0x14d/0x177
 [<c0296a96>] sock_ioctl+0x112/0x2df
 [<c0161e06>] sys_ioctl+0x13a/0x2a0
 [<c0106087>] syscall_call+0x7/0xb
IRQ#3 thread started up.
divert: not allocating divert_blk for non-ethernet device sit0
(IRQ 1/716): new 204218 us maximum-latency critical section.
 => started at: <__do_softirq+0x39/0x59>
 => ended at:   <__do_softirq+0x4a/0x59>
 [<c012f01f>] check_preempt_timing+0x11b/0x1da
 [<c01186d0>] __do_softirq+0x4a/0x59
 [<c01186d0>] __do_softirq+0x4a/0x59
 [<c012f212>] sub_preempt_count+0x4d/0x65
 [<c012f212>] sub_preempt_count+0x4d/0x65
 [<c01186d0>] __do_softirq+0x4a/0x59
 [<c01194d6>] do_irqd+0x71/0x91
 [<c012819f>] kthread+0xaa/0xaf
 [<c0119465>] do_irqd+0x0/0x91
 [<c01280f5>] kthread+0x0/0xaf
 [<c0104215>] kernel_thread_helper+0x5/0xb

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R1

[Ingo Molnar]

* Luke Yelavich <luke@audioslack.com> wrote:

> I think I might be having a problem here, that I didn't have with
> previous patches. Bare in mind that the previous patch I tested was
> against 2.6.8.1 vanilla.
> 
> I am using a D-Link KVM here between my notebook and my desktop
> machine. It is the desktop I am currently testing these patches on,
> and the KVM requires a double-tap of the scroll lock key to switch
> between machines. With the latest R0 patch, something is not working
> when I attempt to change from my desktop to my notebook. The KVM
> usually lets out a beep when I can use the arrow keys to switch, but
> it isn't here. Adding to that, my console locks up totally for about
> 10 seconds, before allowing me to go on and type commands. [...]

i have a KVM too to two testsystems and unfortunately i cannot reproduce
your problems neither with KVM (key-based-)switching nor with scroll
lock. But this KVM uses a triple-key combination to switch, not
scroll-lock.

it's a PS2 keyboard, right? If yes then does:

	echo 0 > /proc/irq/1/i8042/threaded
	( maybe also: echo 0 > /proc/irq/12/i8042/threaded )

fix the problem? The PS2 driver has been a bit unrobust when hardirq
redirection is enabled.

> [...] I also seem to get some debugging output or a trace of some sort
> when rebooting, and the kernel panics with the message: (0)Kernel
> Panic - not syncing: Failed exception in interrupt

hm. Would be nice to get a serial console capture of this, if possible.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R1

[Luke Yelavich]

On Fri, Sep 03, 2004 at 08:29:48PM EST, Ingo Molnar wrote:
> * Luke Yelavich <luke@audioslack.com> wrote:
> > I am using a D-Link KVM here between my notebook and my desktop
> > machine. It is the desktop I am currently testing these patches on,
> > and the KVM requires a double-tap of the scroll lock key to switch
> > between machines. With the latest R0 patch, something is not working
> > when I attempt to change from my desktop to my notebook. The KVM
> > usually lets out a beep when I can use the arrow keys to switch, but
> > it isn't here. Adding to that, my console locks up totally for about
> > 10 seconds, before allowing me to go on and type commands. [...]
> 
> i have a KVM too to two testsystems and unfortunately i cannot reproduce
> your problems neither with KVM (key-based-)switching nor with scroll
> lock. But this KVM uses a triple-key combination to switch, not
> scroll-lock.
> 
> it's a PS2 keyboard, right?

Yes, that is correct.

> If yes then does:
> 
> 	echo 0 > /proc/irq/1/i8042/threaded
> 	( maybe also: echo 0 > /proc/irq/12/i8042/threaded )
> 
> fix the problem? The PS2 driver has been a bit unrobust when hardirq
> redirection is enabled.

I only had to turn off IRQ threading for 1, and all is well again.

> 
> > [...] I also seem to get some debugging output or a trace of some sort
> > when rebooting, and the kernel panics with the message: (0)Kernel
> > Panic - not syncing: Failed exception in interrupt
> 
> hm. Would be nice to get a serial console capture of this, if possible.

I am pretty sure I have a cable, however my desktop is the only computer in this
room that has serial ports, and I also don't know how to set up a serial
console. If you feel that this is important, I will see what I can do.
-- 
Luke Yelavich
http://www.audioslack.com
luke@audioslack.com

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[K.R. Foley]

Ingo Molnar wrote:
> i've released the -R0 patch:
> 
>   http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R0
>  
> ontop of:
> 
>   http://redhat.com/~mingo/voluntary-preempt/diff-bk-040828-2.6.8.1.bz2
> 
> i've given up on the netdev_backlog_granularity approach, and as a
> replacement i've modified specific network drivers to return at a safe
> point if softirq preemption is requested. This gives the same end result
> but is more robust. For the time being i've fixed 8193too.c and e100.c.
> (will fix up other drivers too as latencies get reported)
> 
> this should fix the crash reported by P.O. Gaillard, and it should solve
> the packet delay/loss issues reported by Mark H Johnson. I cannot see
> any problems on my rtl8193 testbox anymore.
> 
> 	Ingo
> 

Last night when rebooting on R0 for the first time, my system locked up. 
It appears to have happened the first time trying to send/recv any real 
data over the e100 interface when ntp was starting up. Will try to 
investigate further a little later.

kr

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R1

[Thomas Charbonnel]

Ingo Molnar wrote :
> Florian Schmidt reported a minor bug that prevents a successful build if
> !CONFIG_LATENCY_TRACE - i've uploaded -R1 that fixes this:
>   
>  http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R1
> 

I still get > 170 us latency from rtl8139 :
http://www.undata.org/~thomas/R1_rtl8139.trace

And again this one :
preemption latency trace v1.0.5 on 2.6.9-rc1-VP-R1
--------------------------------------------------
 latency: 597 us, entries: 12 (12)
    -----------------
    | task: swapper/0, uid:0 nice:0 policy:0 rt_prio:0
    -----------------
 => started at: smp_apic_timer_interrupt+0x32/0xd0
 => ended at:   smp_apic_timer_interrupt+0x86/0xd0
=======>
00010000 0.000ms (+0.000ms): smp_apic_timer_interrupt
(apic_timer_interrupt)
00010000 0.000ms (+0.000ms): profile_tick (smp_apic_timer_interrupt)
00010000 0.000ms (+0.000ms): profile_hook (profile_tick)
00010001 0.000ms (+0.595ms): notifier_call_chain (profile_hook)
00010000 0.595ms (+0.000ms): do_nmi (mcount)
00020000 0.596ms (+0.000ms): profile_tick (nmi_watchdog_tick)
00020000 0.596ms (+0.000ms): profile_hook (profile_tick)
00020001 0.597ms (+0.000ms): notifier_call_chain (profile_hook)
00020000 0.597ms (+689953.444ms): profile_hit (nmi_watchdog_tick)
00010001 689954.042ms (+1.141ms): update_process_times (do_timer)
00000001 0.597ms (+0.000ms): sub_preempt_count
(smp_apic_timer_interrupt)
00000001 0.598ms (+0.000ms): update_max_trace (check_preempt_timing)

Thomas

[patch] voluntary-preempt-2.6.9-rc1-bk4-R2

[Ingo Molnar]

i've uploaded -R2:

  http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R2

no function changes, only fixing some rough edges: it fixes an UP
boot-time assert that occurs right after 'checking hlt'. I also fixed
PREEMPT_TIMING + !LATENCY_TRACE build bugs, and another boot bug that
occurs when PREEMPT_TIMING + !FRAME_POINTERS is used.

(the reboot assert i'm not sure about - tried to reproduce but here
reboot works fine. Will need some sort of serial log to debug this.)

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R1

[Ingo Molnar]

[-- Attachment #1: Type: text/plain, Size: 2395 bytes --]


* Thomas Charbonnel <thomas@undata.org> wrote:

> I still get > 170 us latency from rtl8139 :
> http://www.undata.org/~thomas/R1_rtl8139.trace

this is a single-packet latency, we wont get much lower than this with
the current techniques. Disabling ip_conntrack and tracing ought to
lower the real latency somewhat.

> And again this one :
> preemption latency trace v1.0.5 on 2.6.9-rc1-VP-R1
> --------------------------------------------------
>  latency: 597 us, entries: 12 (12)
>     -----------------
>     | task: swapper/0, uid:0 nice:0 policy:0 rt_prio:0
>     -----------------
>  => started at: smp_apic_timer_interrupt+0x32/0xd0
>  => ended at:   smp_apic_timer_interrupt+0x86/0xd0
> =======>
> 00010000 0.000ms (+0.000ms): smp_apic_timer_interrupt (apic_timer_interrupt)
> 00010000 0.000ms (+0.000ms): profile_tick (smp_apic_timer_interrupt)
> 00010000 0.000ms (+0.000ms): profile_hook (profile_tick)
> 00010001 0.000ms (+0.595ms): notifier_call_chain (profile_hook)
> 00010000 0.595ms (+0.000ms): do_nmi (mcount)
> 00020000 0.596ms (+0.000ms): profile_tick (nmi_watchdog_tick)
> 00020000 0.596ms (+0.000ms): profile_hook (profile_tick)
> 00020001 0.597ms (+0.000ms): notifier_call_chain (profile_hook)
> 00020000 0.597ms (+689953.444ms): profile_hit (nmi_watchdog_tick)
> 00010001 689954.042ms (+1.141ms): update_process_times (do_timer)
> 00000001 0.597ms (+0.000ms): sub_preempt_count (smp_apic_timer_interrupt)
> 00000001 0.598ms (+0.000ms): update_max_trace (check_preempt_timing)

this is a pretty weird one. First it shows an apparently non-monotonic
RDTSC: the jump forward and backward in time around profile_hit. I
suspect the real RDTSC value was lower than the previous one and caused
an underflow. What is your cpu_khz in /proc/cpuinfo?

the other weird one is the +0.595 usec entry at notifier_call_chain(). 
That code is just a couple of instructions, so no real for any overhead 
there.

could you try the attached robust-get-cycles.patch ontop of your current
tree and see whether it impacts these weirdnesses? The patch makes sure
that the cycle counter is sane: two subsequent readings of it were
monotonic and less than 1000 cycles apart.

this patch probably wont remove the +0.595 msec latency though - the
RDTSC value jumped forward there permanently. Maybe the RDTSC value is
somehow corrupted by NMIs - could you turn off the NMI watchdog to
check?

	Ingo

[-- Attachment #2: robust-get-cycles.patch --]
[-- Type: text/plain, Size: 1594 bytes --]

--- linux/kernel/latency.c.orig2	
+++ linux/kernel/latency.c	
@@ -66,6 +66,18 @@ static unsigned long notrace cycles_to_u
 	return (unsigned long) delta;
 }
 
+static cycles_t notrace robust_get_cycles(void)
+{
+	cycles_t t0 = get_cycles(), t1;
+
+	for (;;) {
+		t1 = get_cycles();
+		if (t1 - t0 < 1000)
+			return t1;
+		t0 = t1;
+	}
+}
+
 #ifdef CONFIG_LATENCY_TRACE
 
 unsigned int trace_enabled = 1;
@@ -89,7 +101,7 @@ ____trace(struct cpu_trace *tr, unsigned
 		entry = tr->trace + tr->trace_idx;
 		entry->eip = eip;
 		entry->parent_eip = parent_eip;
-		entry->timestamp = get_cycles();
+		entry->timestamp = robust_get_cycles();
 		entry->preempt_count = preempt_count();
 	}
 	tr->trace_idx++;
@@ -295,7 +307,7 @@ check_preempt_timing(struct cpu_trace *t
 		return;
 #endif
 	atomic_inc(&tr->disabled);
-	latency = cycles_to_usecs(get_cycles() - tr->preempt_timestamp);
+	latency = cycles_to_usecs(robust_get_cycles() - tr->preempt_timestamp);
 
 	if (preempt_thresh) {
 		if (latency < preempt_thresh)
@@ -337,7 +349,7 @@ check_preempt_timing(struct cpu_trace *t
 out:
 #ifdef CONFIG_LATENCY_TRACE
 	tr->trace_idx = 0;
-	tr->preempt_timestamp = get_cycles();
+	tr->preempt_timestamp = robust_get_cycles();
 #endif
 	tr->critical_start = parent_eip;
 	__trace(eip, parent_eip);
@@ -376,7 +388,7 @@ void notrace add_preempt_count(int val)
 		struct cpu_trace *tr = &__get_cpu_var(trace);
 
 		local_irq_save(flags);
-		tr->preempt_timestamp = get_cycles();
+		tr->preempt_timestamp = robust_get_cycles();
 		tr->critical_start = eip;
 #ifdef CONFIG_LATENCY_TRACE
 		tr->trace_idx = 0;

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R1

[Thomas Charbonnel]

Ingo Molnar wrote :
> * Thomas Charbonnel <thomas@undata.org> wrote:
> 
> > I still get > 170 us latency from rtl8139 :
> > http://www.undata.org/~thomas/R1_rtl8139.trace
> 
> this is a single-packet latency, we wont get much lower than this with
> the current techniques. Disabling ip_conntrack and tracing ought to
> lower the real latency somewhat.
> 

Ok, I'll do that.

> > And again this one :
> > preemption latency trace v1.0.5 on 2.6.9-rc1-VP-R1
> > --------------------------------------------------
> >  latency: 597 us, entries: 12 (12)
> >     -----------------
> >     | task: swapper/0, uid:0 nice:0 policy:0 rt_prio:0
> >     -----------------
> >  => started at: smp_apic_timer_interrupt+0x32/0xd0
> >  => ended at:   smp_apic_timer_interrupt+0x86/0xd0
> > =======>
> > 00010000 0.000ms (+0.000ms): smp_apic_timer_interrupt (apic_timer_interrupt)
> > 00010000 0.000ms (+0.000ms): profile_tick (smp_apic_timer_interrupt)
> > 00010000 0.000ms (+0.000ms): profile_hook (profile_tick)
> > 00010001 0.000ms (+0.595ms): notifier_call_chain (profile_hook)
> > 00010000 0.595ms (+0.000ms): do_nmi (mcount)
> > 00020000 0.596ms (+0.000ms): profile_tick (nmi_watchdog_tick)
> > 00020000 0.596ms (+0.000ms): profile_hook (profile_tick)
> > 00020001 0.597ms (+0.000ms): notifier_call_chain (profile_hook)
> > 00020000 0.597ms (+689953.444ms): profile_hit (nmi_watchdog_tick)
> > 00010001 689954.042ms (+1.141ms): update_process_times (do_timer)
> > 00000001 0.597ms (+0.000ms): sub_preempt_count (smp_apic_timer_interrupt)
> > 00000001 0.598ms (+0.000ms): update_max_trace (check_preempt_timing)
> 
> this is a pretty weird one. First it shows an apparently non-monotonic
> RDTSC: the jump forward and backward in time around profile_hit. I
> suspect the real RDTSC value was lower than the previous one and caused
> an underflow. What is your cpu_khz in /proc/cpuinfo?
> 
root@satellite thomas # cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 11
model name      : Intel(R) Pentium(R) III Mobile CPU      1000MHz
stepping        : 1
cpu MHz         : 996.879
cache size      : 512 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 mmx fxsr sse
bogomips        : 1966.08

> the other weird one is the +0.595 usec entry at notifier_call_chain(). 
> That code is just a couple of instructions, so no real for any overhead 
> there.
> 
> could you try the attached robust-get-cycles.patch ontop of your current
> tree and see whether it impacts these weirdnesses? The patch makes sure
> that the cycle counter is sane: two subsequent readings of it were
> monotonic and less than 1000 cycles apart.
> 
> this patch probably wont remove the +0.595 msec latency though - the
> RDTSC value jumped forward there permanently. Maybe the RDTSC value is
> somehow corrupted by NMIs - could you turn off the NMI watchdog to
> check?
> 
> 	Ingo

I precisely enabled the NMI watchdog to track those weird latencies
down. My guess is still that when ACPI is enabled my bios does something
funky with SMM/SMI that increments the TSC. I'll try the patch and let
you know.

Thomas

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Luke Yelavich]

On Fri, Sep 03, 2004 at 06:13:16PM EST, Lee Revell wrote:
> On Fri, 2004-09-03 at 04:09, Luke Yelavich wrote:
> > On Fri, Sep 03, 2004 at 05:40:34PM EST, Lee Revell wrote:
> > > On Fri, 2004-09-03 at 03:05, Ingo Molnar wrote:
> > Well with Lee's help, I think I have identified an ICE1712 sound driver issue,
> > but this is yet to be determined.
> 
> Hmm, this one is still not fixed, using the latest VP patches?

With R2, it turns out that this problem still exists. If I turn off threading
for either ICE1712 soundcard when it is being used by JACK, I get xruns of
around 3 msecs.

I can't remember the info you needed. What is needed to debug this problem?
-- 
Luke Yelavich
http://www.audioslack.com
luke@audioslack.com

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R1

[Thomas Charbonnel]

Ingo Molnar wrote :
> this is a pretty weird one. First it shows an apparently non-monotonic
> RDTSC: the jump forward and backward in time around profile_hit. I
> suspect the real RDTSC value was lower than the previous one and caused
> an underflow. What is your cpu_khz in /proc/cpuinfo?
> 
> the other weird one is the +0.595 usec entry at notifier_call_chain(). 
> That code is just a couple of instructions, so no real for any overhead 
> there.
> 
> could you try the attached robust-get-cycles.patch ontop of your current
> tree and see whether it impacts these weirdnesses? The patch makes sure
> that the cycle counter is sane: two subsequent readings of it were
> monotonic and less than 1000 cycles apart.
> 
> this patch probably wont remove the +0.595 msec latency though - the
> RDTSC value jumped forward there permanently. Maybe the RDTSC value is
> somehow corrupted by NMIs - could you turn off the NMI watchdog to
> check?

Here are more traces with robust-get-cycles applied. So far no
non-monotonic issue.

preemption latency trace v1.0.5 on 2.6.9-rc1-VP-R1
--------------------------------------------------
 latency: 626 us, entries: 25 (25)
    -----------------
    | task: ksoftirqd/0/2, uid:0 nice:-10 policy:0 rt_prio:0
    -----------------
 => started at: preempt_schedule+0x3b/0x60
 => ended at:   schedule+0x2e4/0x570
=======>
04000000 0.000ms (+0.000ms): preempt_schedule (need_resched)
04000000 0.000ms (+0.000ms): schedule (preempt_schedule)
04000001 0.000ms (+0.620ms): sched_clock (schedule)
04010001 0.620ms (+0.000ms): do_nmi (sched_clock)
04010001 0.621ms (+0.000ms): profile_tick (nmi_watchdog_tick)
04010001 0.622ms (+0.000ms): profile_hook (profile_tick)
04010002 0.622ms (+0.000ms): notifier_call_chain (profile_hook)
04010001 0.622ms (+0.000ms): preempt_schedule (profile_tick)
04010001 0.622ms (+0.000ms): profile_hit (nmi_watchdog_tick)
04000001 0.623ms (+0.000ms): smp_apic_timer_interrupt (sched_clock)
04010001 0.623ms (+0.000ms): profile_tick (smp_apic_timer_interrupt)
04010001 0.623ms (+0.000ms): profile_hook (profile_tick)
04010002 0.623ms (+0.000ms): notifier_call_chain (profile_hook)
04010001 0.624ms (+0.000ms): preempt_schedule (profile_tick)
04010001 0.624ms (+0.000ms): profile_hit (smp_apic_timer_interrupt)
04000002 0.624ms (+0.000ms): do_softirq (smp_apic_timer_interrupt)
04000002 0.624ms (+0.000ms): __do_softirq (do_softirq)
04000002 0.625ms (+0.000ms): dequeue_task (schedule)
04000002 0.625ms (+0.000ms): recalc_task_prio (schedule)
04000002 0.625ms (+0.000ms): effective_prio (recalc_task_prio)
04000002 0.625ms (+0.000ms): enqueue_task (schedule)
00000002 0.626ms (+0.000ms): __switch_to (schedule)
00000002 0.626ms (+0.000ms): finish_task_switch (schedule)
00000001 0.626ms (+0.000ms): sub_preempt_count (schedule)
00000001 0.627ms (+0.000ms): update_max_trace (check_preempt_timing)

preemption latency trace v1.0.5 on 2.6.9-rc1-VP-R1
--------------------------------------------------
 latency: 460 us, entries: 38 (38)
    -----------------
    | task: swapper/0, uid:0 nice:0 policy:0 rt_prio:0
    -----------------
 => started at: do_IRQ+0x19/0x190
 => ended at:   do_IRQ+0x14a/0x190
=======>
00010000 0.000ms (+0.000ms): do_IRQ (common_interrupt)
00010000 0.000ms (+0.000ms): do_IRQ (default_idle)
00010000 0.000ms (+0.000ms): do_IRQ (<00000000>)
00010001 0.000ms (+0.444ms): mask_and_ack_8259A (do_IRQ)
00020002 0.444ms (+0.000ms): do_nmi (mask_and_ack_8259A)
00020002 0.445ms (+0.000ms): profile_tick (nmi_watchdog_tick)
00020002 0.446ms (+0.000ms): profile_hook (profile_tick)
00020003 0.446ms (+0.000ms): notifier_call_chain (profile_hook)
00020002 0.446ms (+0.001ms): profile_hit (nmi_watchdog_tick)
00010001 0.448ms (+0.000ms): generic_redirect_hardirq (do_IRQ)
00010000 0.448ms (+0.000ms): generic_handle_IRQ_event (do_IRQ)
00010000 0.448ms (+0.000ms): timer_interrupt (generic_handle_IRQ_event)
00010001 0.448ms (+0.005ms): mark_offset_tsc (timer_interrupt)
00010001 0.454ms (+0.000ms): do_timer (timer_interrupt)
00010001 0.454ms (+0.000ms): update_process_times (do_timer)
00010001 0.454ms (+0.000ms): update_one_process (update_process_times)
00010001 0.455ms (+0.000ms): run_local_timers (update_process_times)
00010001 0.455ms (+0.000ms): raise_softirq (update_process_times)
00010001 0.455ms (+0.000ms): scheduler_tick (update_process_times)
00010001 0.455ms (+0.000ms): sched_clock (scheduler_tick)
00010001 0.456ms (+0.000ms): update_wall_time (do_timer)
00010001 0.456ms (+0.000ms): update_wall_time_one_tick
(update_wall_time)
00010001 0.456ms (+0.000ms): generic_note_interrupt (do_IRQ)
00010001 0.456ms (+0.000ms): end_8259A_irq (do_IRQ)
00010001 0.457ms (+0.001ms): enable_8259A_irq (do_IRQ)
00000001 0.458ms (+0.000ms): do_softirq (do_IRQ)
00000001 0.458ms (+0.000ms): __do_softirq (do_softirq)
00000001 0.458ms (+0.000ms): wake_up_process (do_softirq)
00000001 0.458ms (+0.000ms): try_to_wake_up (wake_up_process)
00000001 0.458ms (+0.000ms): task_rq_lock (try_to_wake_up)
00000002 0.459ms (+0.000ms): activate_task (try_to_wake_up)
00000002 0.459ms (+0.000ms): sched_clock (activate_task)
00000002 0.459ms (+0.000ms): recalc_task_prio (activate_task)
00000002 0.459ms (+0.000ms): effective_prio (recalc_task_prio)
00000002 0.459ms (+0.000ms): enqueue_task (activate_task)
00000001 0.460ms (+0.000ms): preempt_schedule (try_to_wake_up)
00000001 0.460ms (+0.000ms): sub_preempt_count (do_IRQ)
00000001 0.460ms (+0.000ms): update_max_trace (check_preempt_timing)

preemption latency trace v1.0.5 on 2.6.9-rc1-VP-R1
--------------------------------------------------
 latency: 557 us, entries: 39 (39)
    -----------------
    | task: evolution-1.4/5492, uid:1000 nice:0 policy:0 rt_prio:0
    -----------------
 => started at: fget+0x32/0x80
 => ended at:   fget+0x58/0x80
=======>
00000001 0.000ms (+0.537ms): fget (do_pollfd)
00010001 0.537ms (+0.000ms): do_nmi (sub_preempt_count)
00010001 0.538ms (+0.000ms): profile_tick (nmi_watchdog_tick)
00010001 0.538ms (+0.000ms): profile_hook (profile_tick)
00010002 0.539ms (+0.000ms): notifier_call_chain (profile_hook)
00010001 0.539ms (+0.001ms): profile_hit (nmi_watchdog_tick)
00010001 0.540ms (+0.000ms): do_IRQ (sub_preempt_count)
00010001 0.540ms (+0.000ms): do_IRQ (<00000000>)
00010002 0.541ms (+0.002ms): mask_and_ack_8259A (do_IRQ)
00010002 0.543ms (+0.000ms): generic_redirect_hardirq (do_IRQ)
00010001 0.543ms (+0.000ms): generic_handle_IRQ_event (do_IRQ)
00010001 0.543ms (+0.000ms): timer_interrupt (generic_handle_IRQ_event)
00010002 0.544ms (+0.005ms): mark_offset_tsc (timer_interrupt)
00010002 0.549ms (+0.000ms): do_timer (timer_interrupt)
00010002 0.550ms (+0.000ms): update_process_times (do_timer)
00010002 0.550ms (+0.000ms): update_one_process (update_process_times)
00010002 0.550ms (+0.000ms): run_local_timers (update_process_times)
00010002 0.550ms (+0.000ms): raise_softirq (update_process_times)
00010002 0.551ms (+0.000ms): scheduler_tick (update_process_times)
00010002 0.551ms (+0.000ms): sched_clock (scheduler_tick)
00010003 0.551ms (+0.000ms): task_timeslice (scheduler_tick)
00010002 0.552ms (+0.000ms): update_wall_time (do_timer)
00010002 0.552ms (+0.000ms): update_wall_time_one_tick
(update_wall_time)
00010002 0.552ms (+0.000ms): generic_note_interrupt (do_IRQ)
00010002 0.553ms (+0.000ms): end_8259A_irq (do_IRQ)
00010002 0.553ms (+0.001ms): enable_8259A_irq (do_IRQ)
00000002 0.554ms (+0.000ms): do_softirq (do_IRQ)
00000002 0.554ms (+0.000ms): __do_softirq (do_softirq)
00000002 0.554ms (+0.000ms): wake_up_process (do_softirq)
00000002 0.555ms (+0.000ms): try_to_wake_up (wake_up_process)
00000002 0.555ms (+0.000ms): task_rq_lock (try_to_wake_up)
00000003 0.555ms (+0.000ms): activate_task (try_to_wake_up)
00000003 0.555ms (+0.000ms): sched_clock (activate_task)
00000003 0.555ms (+0.000ms): recalc_task_prio (activate_task)
00000003 0.556ms (+0.000ms): effective_prio (recalc_task_prio)
00000003 0.556ms (+0.000ms): enqueue_task (activate_task)
00000002 0.556ms (+0.000ms): preempt_schedule (try_to_wake_up)
00000001 0.557ms (+0.000ms): sub_preempt_count (fget)
00000001 0.557ms (+0.000ms): update_max_trace (check_preempt_timing)

I had similar problems affecting apparently random code paths before
enabling nmi_watchdog, but if you feel it can be useful, I can do some
more tests with robust-get-cycles and without nmi.

Thomas

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[K.R. Foley]

Ingo Molnar wrote:
> i've released the -R0 patch:
> 
>   http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R0
>  
> ontop of:
> 
>   http://redhat.com/~mingo/voluntary-preempt/diff-bk-040828-2.6.8.1.bz2
> 
> i've given up on the netdev_backlog_granularity approach, and as a
> replacement i've modified specific network drivers to return at a safe
> point if softirq preemption is requested. This gives the same end result
> but is more robust. For the time being i've fixed 8193too.c and e100.c.
> (will fix up other drivers too as latencies get reported)
> 
> this should fix the crash reported by P.O. Gaillard, and it should solve
> the packet delay/loss issues reported by Mark H Johnson. I cannot see
> any problems on my rtl8193 testbox anymore.
> 
> 	Ingo
> 

OK. I previously reported about the system hanging trying to boot this 
patch. It may have been a fluke. In any event, it doesn't hang 
consistently. I have rebooted several times now without problems. I do 
however still get some of these:

(ksoftirqd/0/2): new 131 us maximum-latency critical section.
  => started at: <netif_receive_skb+0x82/0x280>
  => ended at:   <netif_receive_skb+0x1d7/0x280>
  [<c0136789>] check_preempt_timing+0x119/0x1f0
  [<c0255017>] netif_receive_skb+0x1d7/0x280
  [<c0255017>] netif_receive_skb+0x1d7/0x280
  [<c013699d>] sub_preempt_count+0x4d/0x70
  [<c013699d>] sub_preempt_count+0x4d/0x70
  [<c0255017>] netif_receive_skb+0x1d7/0x280
  [<d08d40b7>] e100_poll+0x5b7/0x630 [e100]
  [<c013699d>] sub_preempt_count+0x4d/0x70
  [<c025527f>] net_rx_action+0x7f/0x110
  [<c011eb55>] ___do_softirq+0x75/0x90
  [<c011ec1e>] _do_softirq+0xe/0x20
  [<c011f034>] ksoftirqd+0x94/0xe0
  [<c012f8aa>] kthread+0xaa/0xb0
  [<c011efa0>] ksoftirqd+0x0/0xe0
  [<c012f800>] kthread+0x0/0xb0
  [<c0104575>] kernel_thread_helper+0x5/0x10

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[K.R. Foley]

Ingo Molnar wrote:
> i've released the -R0 patch:
> 
>   http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R0
>  
> ontop of:
> 
>   http://redhat.com/~mingo/voluntary-preempt/diff-bk-040828-2.6.8.1.bz2
> 

Managed to hang the system again under heavy load. This time with the 
above patch:

http://www.cybsft.com/testresults/crashes/2.6.9-rc1-bk4-R0.txt

Last time was with Q7:

http://www.cybsft.com/testresults/crashes/2.6.9-rc1-bk4-Q7.txt


kr

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R1

[Thomas Charbonnel]

I wrote :
> Ingo Molnar wrote :
> > this is a pretty weird one. First it shows an apparently non-monotonic
> > RDTSC: the jump forward and backward in time around profile_hit. I
> > suspect the real RDTSC value was lower than the previous one and caused
> > an underflow. What is your cpu_khz in /proc/cpuinfo?
> > 
> > the other weird one is the +0.595 usec entry at notifier_call_chain(). 
> > That code is just a couple of instructions, so no real for any overhead 
> > there.
> > 
> > could you try the attached robust-get-cycles.patch ontop of your current
> > tree and see whether it impacts these weirdnesses? The patch makes sure
> > that the cycle counter is sane: two subsequent readings of it were
> > monotonic and less than 1000 cycles apart.
> > 
> > this patch probably wont remove the +0.595 msec latency though - the
> > RDTSC value jumped forward there permanently. Maybe the RDTSC value is
> > somehow corrupted by NMIs - could you turn off the NMI watchdog to
> > check?
> 
> Here are more traces with robust-get-cycles applied. So far no
> non-monotonic issue.

In the end here's one :

preemption latency trace v1.0.5 on 2.6.9-rc1-VP-R1
--------------------------------------------------
 latency: 891 us, entries: 38 (38)
    -----------------
    | task: swapper/0, uid:0 nice:0 policy:0 rt_prio:0
    -----------------
 => started at: do_IRQ+0x19/0x190
 => ended at:   do_IRQ+0x14a/0x190
=======>
00010000 0.000ms (+0.876ms): do_nmi (robust_get_cycles)
00020000 0.876ms (+0.000ms): profile_tick (nmi_watchdog_tick)
00020000 0.876ms (+0.000ms): profile_hook (profile_tick)
00020001 0.876ms (+0.000ms): notifier_call_chain (profile_hook)
00020000 0.876ms (+689952.730ms): profile_hit (nmi_watchdog_tick)
04000002 689953.607ms (+1.855ms): finish_task_switch (schedule)
00010000 0.877ms (+0.000ms): do_IRQ (default_idle)
00010000 0.877ms (+0.000ms): do_IRQ (<00000000>)
00010001 0.877ms (+0.002ms): mask_and_ack_8259A (do_IRQ)
00010001 0.879ms (+0.000ms): generic_redirect_hardirq (do_IRQ)
00010000 0.880ms (+0.000ms): generic_handle_IRQ_event (do_IRQ)
00010000 0.880ms (+0.000ms): timer_interrupt (generic_handle_IRQ_event)
00010001 0.880ms (+0.005ms): mark_offset_tsc (timer_interrupt)
00010001 0.886ms (+0.000ms): do_timer (timer_interrupt)
00010001 0.886ms (+0.000ms): update_process_times (do_timer)
00010001 0.886ms (+0.000ms): update_one_process (update_process_times)
00010001 0.886ms (+0.000ms): run_local_timers (update_process_times)
00010001 0.886ms (+0.000ms): raise_softirq (update_process_times)
00010001 0.887ms (+0.000ms): scheduler_tick (update_process_times)
00010001 0.887ms (+0.000ms): sched_clock (scheduler_tick)
00010001 0.887ms (+0.000ms): update_wall_time (do_timer)
00010001 0.887ms (+0.000ms): update_wall_time_one_tick
(update_wall_time)
00010001 0.888ms (+0.000ms): generic_note_interrupt (do_IRQ)
00010001 0.888ms (+0.000ms): end_8259A_irq (do_IRQ)
00010001 0.888ms (+0.001ms): enable_8259A_irq (do_IRQ)
00000001 0.889ms (+0.000ms): do_softirq (do_IRQ)
00000001 0.889ms (+0.000ms): __do_softirq (do_softirq)
00000001 0.889ms (+0.000ms): wake_up_process (do_softirq)
00000001 0.890ms (+0.000ms): try_to_wake_up (wake_up_process)
00000001 0.890ms (+0.000ms): task_rq_lock (try_to_wake_up)
00000002 0.890ms (+0.000ms): activate_task (try_to_wake_up)
00000002 0.890ms (+0.000ms): sched_clock (activate_task)
00000002 0.890ms (+0.000ms): recalc_task_prio (activate_task)
00000002 0.891ms (+0.000ms): effective_prio (recalc_task_prio)
00000002 0.891ms (+0.000ms): enqueue_task (activate_task)
00000001 0.891ms (+0.000ms): preempt_schedule (try_to_wake_up)
00000001 0.892ms (+0.000ms): sub_preempt_count (do_IRQ)
00000001 0.892ms (+0.000ms): update_max_trace (check_preempt_timing)

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[K.R. Foley]

Ingo Molnar wrote:
> another question - any objections against me rebasing the VP patch to
> the current -mm tree and keeping it there exclusively until all possible
> merges are done? It would probably quite some work to create a complete
> patch for the upstream or BK tree during that process, as small patches
> start to flow in the VP => -mm => BK direction. Would any of the regular
> VP users/testers be wary to use the -mm tree?
> 
> 	Ingo
> 

I don't have any objections. Should I be wary of running the -mm tree?

kr

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Ingo Molnar]

* K.R. Foley <kr@cybsft.com> wrote:

> Managed to hang the system again under heavy load. This time with the
> above patch:
> 
> http://www.cybsft.com/testresults/crashes/2.6.9-rc1-bk4-R0.txt
> 
> Last time was with Q7:
> 
> http://www.cybsft.com/testresults/crashes/2.6.9-rc1-bk4-Q7.txt

seems to be the same thing - an unbalanced preemption count, possibly
due to some locking error. Unfortunately the assert catches the
imbalance only at exit time. (it's unlikely that the do_exit() code is
buggy.)

i'll add a new feature to debug this: when crashing on an assert and
tracing is enabled the trace leading up to the crash will be printed to
the console. How did you capture the crash - was it in the syslog or do
you have serial logging? Maybe this is not the real crash but only a
followup crash?

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[K.R. Foley]

Ingo Molnar wrote:
> * K.R. Foley <kr@cybsft.com> wrote:
> 
> 
>>Managed to hang the system again under heavy load. This time with the
>>above patch:
>>
>>http://www.cybsft.com/testresults/crashes/2.6.9-rc1-bk4-R0.txt
>>
>>Last time was with Q7:
>>
>>http://www.cybsft.com/testresults/crashes/2.6.9-rc1-bk4-Q7.txt
> 
> 
> seems to be the same thing - an unbalanced preemption count, possibly
> due to some locking error. Unfortunately the assert catches the
> imbalance only at exit time. (it's unlikely that the do_exit() code is
> buggy.)
> 
> i'll add a new feature to debug this: when crashing on an assert and
> tracing is enabled the trace leading up to the crash will be printed to
> the console. How did you capture the crash - was it in the syslog or do
> you have serial logging? Maybe this is not the real crash but only a
> followup crash?
> 
> 	Ingo
> 

This actually came from syslog. When it happened it was completely 
locked, so I have no idea if there was more that didn't make it to disk. 
Of course the monitor was blanked because most of the access is via the 
network. I could probably enable serial logging if necessary because 
it's sitting next to a couple of other machines.

kr

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Ingo Molnar]

* K.R. Foley <kr@cybsft.com> wrote:

> Managed to hang the system again under heavy load. This time with the 
> above patch:
> 
> http://www.cybsft.com/testresults/crashes/2.6.9-rc1-bk4-R0.txt

do you have CONFIG_DEBUG_SPINLOCK and CONFIG_DEBUG_SPINLOCK_SLEEP
enabled? These are pretty good at e.g. catching illegal scheduling in
critical sections much earlier. You can enable them on !SMP kernels as
well.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[K.R. Foley]

Ingo Molnar wrote:
> * K.R. Foley <kr@cybsft.com> wrote:
> 
> 
>>Managed to hang the system again under heavy load. This time with the 
>>above patch:
>>
>>http://www.cybsft.com/testresults/crashes/2.6.9-rc1-bk4-R0.txt
> 
> 
> do you have CONFIG_DEBUG_SPINLOCK and CONFIG_DEBUG_SPINLOCK_SLEEP
> enabled? These are pretty good at e.g. catching illegal scheduling in
> critical sections much earlier. You can enable them on !SMP kernels as
> well.
> 
> 	Ingo

Not currently but I am enabling now.

kr

[patch] voluntary-preempt-2.6.9-rc1-bk4-R3

[Ingo Molnar]

* Ingo Molnar <mingo@elte.hu> wrote:

> i'll add a new feature to debug this: when crashing on an assert and
> tracing is enabled the trace leading up to the crash will be printed
> to the console. [...]

the -R3 patch has this feature:

  http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R3 

you can enable it via enabling CONFIG_LATENCY_TRACE and doing:

  echo 3 > /proc/sys/kernel/trace_enabled

it's all automatic from this point on: tracing will happen nonstop and
any assert or crash that prints the process stack will also print the
last 100 trace entries. Sample output:

 Call Trace:
  [<c0160401>] sys_munmap+0x61/0x80
  [<c010520d>] sysenter_past_esp+0x52/0x71
 Last 100 trace entries:
 00000001: zap_pmd_range+0xe/0x90  <= (unmap_page_range+0x55/0x80)
 00000001: stop_trace+0x8/0x20  <= (bust_spinlocks+0x20/0x60)
 00000001: bust_spinlocks+0xe/0x60  <= (die+0xbc/0x2a0)
 [... 97 more trace entries ...]

Please capture and mail the first 'extended' oops that triggers
(secondary followup traces are probably just side-effects of the crash),
it could give us clues about where the bug is.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R3

[K.R. Foley]

Ingo Molnar wrote:
> * Ingo Molnar <mingo@elte.hu> wrote:
> 
> 
>>i'll add a new feature to debug this: when crashing on an assert and
>>tracing is enabled the trace leading up to the crash will be printed
>>to the console. [...]
> 
> 
> the -R3 patch has this feature:
> 
>   http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R3 
> 
> you can enable it via enabling CONFIG_LATENCY_TRACE and doing:
> 
>   echo 3 > /proc/sys/kernel/trace_enabled
> 
> it's all automatic from this point on: tracing will happen nonstop and
> any assert or crash that prints the process stack will also print the
> last 100 trace entries. Sample output:
> 
>  Call Trace:
>   [<c0160401>] sys_munmap+0x61/0x80
>   [<c010520d>] sysenter_past_esp+0x52/0x71
>  Last 100 trace entries:
>  00000001: zap_pmd_range+0xe/0x90  <= (unmap_page_range+0x55/0x80)
>  00000001: stop_trace+0x8/0x20  <= (bust_spinlocks+0x20/0x60)
>  00000001: bust_spinlocks+0xe/0x60  <= (die+0xbc/0x2a0)
>  [... 97 more trace entries ...]
> 
> Please capture and mail the first 'extended' oops that triggers
> (secondary followup traces are probably just side-effects of the crash),
> it could give us clues about where the bug is.
> 
> 	Ingo
> 

Building now.

kr

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

[Lee Revell]

On Fri, 2004-09-03 at 13:02, K.R. Foley wrote:
> OK. I previously reported about the system hanging trying to boot this 
> patch. It may have been a fluke. In any event, it doesn't hang 
> consistently. I have rebooted several times now without problems. I do 
> however still get some of these:
> 
> (ksoftirqd/0/2): new 131 us maximum-latency critical section.
>   => started at: <netif_receive_skb+0x82/0x280>
>   => ended at:   <netif_receive_skb+0x1d7/0x280>

This is actually a good sign if this is the most common one you see. 
The netif_receive softirq is basically the longest code path that can't
easily be made preemptible; on my hardware about 150 usecs seems to be
the best we can do.  This is really good, I can't imagine an application
that you would use PC hardware for where 150 usecs is not enough, though
I am sure the hard realtime crowd has a few.

Even fixing this one would not help much because it seems there are many
other non-preemtible code paths that are only a little shorter than this
one.

Lee

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R3

[K.R. Foley]

Ingo Molnar wrote:
> * Ingo Molnar <mingo@elte.hu> wrote:
> 
> 
>>i'll add a new feature to debug this: when crashing on an assert and
>>tracing is enabled the trace leading up to the crash will be printed
>>to the console. [...]
> 
> 
> the -R3 patch has this feature:
> 

After hammering the system for a little more than an hour it gave up. I 
don't have the serial logging setup yet because I haven't had time this 
evening. I will be glad to do whatever I can to try to help debug this, 
but it will have to wait until tomorrow. The log is here:

http://www.cybsft.com/testresults/crashes/2.6.9-rc1-vo-R3.txt

kr

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R3

[K.R. Foley]

Ingo Molnar wrote:
> * Ingo Molnar <mingo@elte.hu> wrote:
> 
> 
>>i'll add a new feature to debug this: when crashing on an assert and
>>tracing is enabled the trace leading up to the crash will be printed
>>to the console. [...]
> 
> 
> the -R3 patch has this feature:
> 

After hammering the system for a little more than an hour it gave up. I
don't have the serial logging setup yet because I haven't had time this
evening. I will be glad to do whatever I can to try to help debug this,
but it will have to wait until tomorrow. The log is here:

http://www.cybsft.com/testresults/crashes/2.6.9-rc1-vo-R3.txt

kr

Sorry I forgot to mention that this was triggered running the 
stress-kernel package, minus the NFS-Compile, but it does include the 
CRASHME test. In addition, amlat was running as well. The system was 
pretty much 100% loaded.

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R3

[Ingo Molnar]

* K.R. Foley <kr@cybsft.com> wrote:

> http://www.cybsft.com/testresults/crashes/2.6.9-rc1-vo-R3.txt

the first line seems partial - isnt the full oops in the log?

> Sorry I forgot to mention that this was triggered running the
> stress-kernel package, minus the NFS-Compile, but it does include the
> CRASHME test. In addition, amlat was running as well. The system was
> pretty much 100% loaded.

Have you run crashme as root? That would be unsafe.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R3

[Ingo Molnar]

* K.R. Foley <kr@cybsft.com> wrote:

> After hammering the system for a little more than an hour it gave up.
> I don't have the serial logging setup yet because I haven't had time
> this evening. I will be glad to do whatever I can to try to help debug
> this, but it will have to wait until tomorrow. The log is here:
> 
> http://www.cybsft.com/testresults/crashes/2.6.9-rc1-vo-R3.txt

fyi, i have now triggered a similar crash on a testbox too. It takes
quite some time to trigger but it does.

since it happens with VP=0,KP=0,SP=0,HP=0 as well it should be one of
the cond_resched_lock() (or cond_resched()) additions.

	Ingo

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R3

[Lee Revell]

On Sat, 2004-09-04 at 04:57, Ingo Molnar wrote:
> * K.R. Foley <kr@cybsft.com> wrote:
> 
> > After hammering the system for a little more than an hour it gave up.
> > I don't have the serial logging setup yet because I haven't had time
> > this evening. I will be glad to do whatever I can to try to help debug
> > this, but it will have to wait until tomorrow. The log is here:
> > 
> > http://www.cybsft.com/testresults/crashes/2.6.9-rc1-vo-R3.txt
> 
> fyi, i have now triggered a similar crash on a testbox too. It takes
> quite some time to trigger but it does.
> 
> since it happens with VP=0,KP=0,SP=0,HP=0 as well it should be one of
> the cond_resched_lock() (or cond_resched()) additions.
> 

Here are some results for R0 on another machine, a 1.2Ghz Athlon XP:

http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-R0

I have also changed the test again, to be more accurate.  Now the jackd
alsa driver separately keeps track of the time it spends in poll(), and
the time it takes running the jackd process cycle.  The length of one
period less the sum of the time we spent in poll() and the time it took
to run the process cycle equals the amount of time we spent ready to
run, and waiting to be scheduled AKA latency.

The results are pretty amazing - out of a period time of 666 usecs most
of the time we spend between 0 and 1 usec in this state,  The worst is
27 usecs or so.

These results are of course not directly comparable with previous tests,
but I believe this is the most accurate way to measure latency in jackd.

Lee 

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R3

[K.R. Foley]

Ingo Molnar wrote:
> * K.R. Foley <kr@cybsft.com> wrote:
> 
> 
>>http://www.cybsft.com/testresults/crashes/2.6.9-rc1-vo-R3.txt
> 
> 
> the first line seems partial - isnt the full oops in the log?

Agreed. Unfortunately that is all there is.

> 
> 
>>Sorry I forgot to mention that this was triggered running the
>>stress-kernel package, minus the NFS-Compile, but it does include the
>>CRASHME test. In addition, amlat was running as well. The system was
>>pretty much 100% loaded.
> 
> 
> Have you run crashme as root? That would be unsafe.

Actually what happens is that it creates a "crashme" user (and group)
for running the test and then deletes the user after the test. In fact
the user is still in passwd, because of the crash it didn't get cleaned
up. So I don't think this SHOULD be a problem.

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R3

[K.R. Foley]

Ingo Molnar wrote:
> * K.R. Foley <kr@cybsft.com> wrote:
> 
> 
>>After hammering the system for a little more than an hour it gave up.
>>I don't have the serial logging setup yet because I haven't had time
>>this evening. I will be glad to do whatever I can to try to help debug
>>this, but it will have to wait until tomorrow. The log is here:
>>
>>http://www.cybsft.com/testresults/crashes/2.6.9-rc1-vo-R3.txt
> 
> 
> fyi, i have now triggered a similar crash on a testbox too. It takes
> quite some time to trigger but it does.
> 
> since it happens with VP=0,KP=0,SP=0,HP=0 as well it should be one of
> the cond_resched_lock() (or cond_resched()) additions.
> 
> 	Ingo
> 

I am glad that it's reproducible for you as well. How did you trigger 
it? Because it seems to only crash under heavy load for me. The system 
has been up since I rebooted last night after the crash and I haven't 
seen any problems. Same thing goes for up until last night when I booted 
the new patch. Even building the new patch didn't seem to be enough to 
trigger it.

kr

Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R3

[Ingo Molnar]

* K.R. Foley <kr@cybsft.com> wrote:

> I am glad that it's reproducible for you as well. How did you trigger
> it? Because it seems to only crash under heavy load for me. The system
> has been up since I rebooted last night after the crash and I haven't
> seen any problems. Same thing goes for up until last night when I
> booted the new patch. Even building the new patch didn't seem to be
> enough to trigger it.

i triggered it via two IO-intense scripts running on a 256 MB RAM
testbox:

  cd /tmp; while true; do dd if=/dev/zero of=bigfile bs=1000000 
  count=500 >/dev/null 2>/dev/null; sync; date; sleep 60; done &

  while true; do du /usr >/dev/null 2>/dev/null; date; done &

usually it triggers within half an hour or so of runtime. With -R4 it
didnt crash yet after ~1 hour of running so i'm quite optimistic that 
this particular bug has been fixed.

i think the key to reproduce was to use KP=0,SP=0,HP=0 - this
concentrates all preemption activity to the places the VP patch adds -
amongst them the one in the do_exit() path that is necessary to trigger
the race.

	Ingo