Re: [Lse-tech] Re: CPU affinity & IPI latency (FIX)_

Hubertus Franke
2001-07-17T18:14:37Z

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David, thanks for pointing this out. Ofcourse, it has be reset at that point.
Since it is still running, it actually proves that priority overwrites for
reservations work.
Did you have a chance to run it on the offending app. I don't have that one,
hence I only tried on kernel builds etc.
Here is the update patch.

-- Hubertus (frankeh@us.ibm.com)

> Davide Libenzi <davidel@xmailserver.org>@lists.sourceforge.net on
> 07/17/2001 02:00:45 PM
>
> Sent by: lse-tech-admin@lists.sourceforge.net
>
> To: Hubertus Frnake <frankeh@watson.ibm.com>
> cc: linux-kernel@vger.kernel.org, lse-tech@lists.sourceforge.net,
> ak@suse.de
> Subject: Re: [Lse-tech] Re: CPU affinity & IPI latency (FIX)_
>
> On 17-Jul-2001 Hubertus Frnake wrote:
> > In an attempt to inline the code, somehow the tabs got lost. So here is
> the
> > attached correct patch fo 2.4.5. Please try and let me know whether you
> > see your problems disappear and/or others arise.
> > The sketchy writeup is still the same.
>
> Did You tried the patch ?
> Maybe this could help :
>
> + next = cpu_resched(this_cpu);
> + if (next) {
> + cpu_resched(this_cpu) = NULL;
> - next = p;
> + goto found_next;
> + }
>
> - Davide
>
> _______________________________________________
> Lse-tech mailing list
> Lse-tech@lists.sourceforge.net
> http://lists.sourceforge.net/lists/listinfo/lse-tech

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diff -uwrbBN linux-2.4.5-van/kernel/sched.c linux-2.4.5-ca/kernel/sched.c
--- linux-2.4.5-van/kernel/sched.c Fri Apr 20 21:26:16 2001
+++ linux-2.4.5-ca/kernel/sched.c Tue Jul 17 14:02:13 2001
@@ -97,12 +97,14 @@
static union {
struct schedule_data {
struct task_struct * curr;
+ struct task_struct * resched;
cycles_t last_schedule;
} schedule_data;
char __pad [SMP_CACHE_BYTES];
-} aligned_data [NR_CPUS] __cacheline_aligned = { {{&init_task,0}}};
+} aligned_data [NR_CPUS] __cacheline_aligned = { {{&init_task,0,0}}};

#define cpu_curr(cpu) aligned_data[(cpu)].schedule_data.curr
+#define cpu_resched(cpu) aligned_data[(cpu)].schedule_data.resched
#define last_schedule(cpu) aligned_data[(cpu)].schedule_data.last_schedule

struct kernel_stat kstat;
@@ -208,7 +210,7 @@
{
#ifdef CONFIG_SMP
int this_cpu = smp_processor_id();
- struct task_struct *tsk, *target_tsk;
+ struct task_struct *tsk, *target_tsk, *rtsk;
int cpu, best_cpu, i, max_prio;
cycles_t oldest_idle;

@@ -219,7 +221,9 @@
best_cpu = p->processor;
if (can_schedule(p, best_cpu)) {
tsk = idle_task(best_cpu);
- if (cpu_curr(best_cpu) == tsk) {
+ if ((cpu_curr(best_cpu) == tsk) &&
+ (cpu_resched(best_cpu) == NULL))
+ {
int need_resched;
send_now_idle:
/*
@@ -244,13 +248,24 @@
*/
oldest_idle = (cycles_t) -1;
target_tsk = NULL;
+ best_cpu = 0;
max_prio = 1;

for (i = 0; i < smp_num_cpus; i++) {
cpu = cpu_logical_map(i);
if (!can_schedule(p, cpu))
continue;
+ /* first check whether there is an resched IPI
+ * reservation for that cpu. If so consider priority
+ * of the reservation instead of current.
+ * We do not have to set the need_resched flag again
+ * for the currently running task. It must have been
+ * signalled before
+ */
+ tsk = cpu_resched(cpu);
+ if (tsk == NULL)
tsk = cpu_curr(cpu);
+
/*
* We use the first available idle CPU. This creates
* a priority list between idle CPUs, but this is not
@@ -268,19 +283,30 @@
if (prio > max_prio) {
max_prio = prio;
target_tsk = tsk;
+ best_cpu = cpu;
}
}
}
}
tsk = target_tsk;
if (tsk) {
+ rtsk = cpu_resched(best_cpu);
+ if (rtsk) {
+ rtsk->has_cpu = 0; /* return rtsk to scheduable */
+ tsk->has_cpu = 1; /* can't schedule this one no more*/
+ cpu_resched(best_cpu) = tsk;
+ return;
+ }
if (oldest_idle != -1ULL) {
best_cpu = tsk->processor;
goto send_now_idle;
}
tsk->need_resched = 1;
- if (tsk->processor != this_cpu)
- smp_send_reschedule(tsk->processor);
+ if (tsk->processor != this_cpu) {
+ tsk->has_cpu = 1;
+ cpu_resched(best_cpu) = tsk;
+ smp_send_reschedule(best_cpu);
+ }
}
return;

@@ -578,6 +604,16 @@
*/

repeat_schedule:
+ /* we check whether we have a resched_IPI reservation:
+ * if so simply select the reserving task and next and
+ * go to switch to it.
+ */
+ next = cpu_resched(this_cpu);
+ if (next) {
+ cpu_resched(this_cpu) = NULL;
+ next = p;
+ goto found_next;
+ }
/*
* Default process to select..
*/
@@ -604,6 +640,7 @@
* switching to the next task, save this fact in
* sched_data.
*/
+found_next:
sched_data->curr = next;
#ifdef CONFIG_SMP
next->has_cpu = 1;