Re: [patch 0/2] NOHZ vs. profile/oprofile v2

Martin Schwidefsky
2009-06-22T14:27:13Z

On Tue, 9 Jun 2009 22:52:51 +0200 (CEST)
Thomas Gleixner <tglx@linutronix.de> wrote:

> > version 2 of the profile patches. The only change is the in_interrupt()
> > fix in tick_nohz_stop_idle(). I would like to know how to proceed with
> > the issue.
> > Andy, do you still prefer to handle the old style profiler analog to
> > the oprofile patch? If yes I would drop patch #1 and extend patch #2
> > with another tick_nohz_disable().
>
> Any update on this one ?

A solution to this problem should go upstream soon, no? How about this
patch, it uses the tick_nohz_disable/tick_nohz_enable mechanic for
oprofile and the old style kernel profiler. Good enough ?

---
Subject: [PATCH] keep on ticking if a profiler is active

From: Martin Schwidefsky <schwidefsky@de.ibm.com>

On a NOHZ system with oprofile or the old style kernel profiler enabled
the timer tick should not be stopped when a cpu goes idle. Currently
a maximum of 1 tick is accounted if a cpu sleeps for a longer period of
time. This does bad things to the percentages in the profiler output.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---

drivers/oprofile/oprof.c | 3 +++
include/linux/tick.h | 4 ++++
kernel/profile.c | 4 ++++
kernel/time/tick-sched.c | 27 ++++++++++++++++++++++++++-
4 files changed, 37 insertions(+), 1 deletion(-)

diff -urpN linux-2.6/drivers/oprofile/oprof.c linux-2.6-patched/drivers/oprofile/oprof.c
--- linux-2.6/drivers/oprofile/oprof.c 2009-06-10 05:05:27.000000000 +0200
+++ linux-2.6-patched/drivers/oprofile/oprof.c 2009-06-22 11:26:50.000000000 +0200
@@ -12,6 +12,7 @@
#include <linux/init.h>
#include <linux/oprofile.h>
#include <linux/moduleparam.h>
+#include <linux/tick.h>
#include <asm/mutex.h>

#include "oprof.h"
@@ -103,6 +104,7 @@ int oprofile_start(void)
if (oprofile_started)
goto out;

+ tick_nohz_disable(1);
oprofile_reset_stats();

if ((err = oprofile_ops.start()))
@@ -123,6 +125,7 @@ void oprofile_stop(void)
goto out;
oprofile_ops.stop();
oprofile_started = 0;
+ tick_nohz_enable();
/* wake up the daemon to read what remains */
wake_up_buffer_waiter();
out:
diff -urpN linux-2.6/include/linux/tick.h linux-2.6-patched/include/linux/tick.h
--- linux-2.6/include/linux/tick.h 2009-06-22 11:26:26.000000000 +0200
+++ linux-2.6-patched/include/linux/tick.h 2009-06-22 11:26:50.000000000 +0200
@@ -119,6 +119,8 @@ extern void tick_nohz_stop_sched_tick(in
extern void tick_nohz_restart_sched_tick(void);
extern ktime_t tick_nohz_get_sleep_length(void);
extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
+extern void tick_nohz_enable(void);
+extern void tick_nohz_disable(int wakeup);
# else
static inline void tick_nohz_stop_sched_tick(int inidle) { }
static inline void tick_nohz_restart_sched_tick(void) { }
@@ -129,6 +131,8 @@ static inline ktime_t tick_nohz_get_slee
return len;
}
static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; }
+static inline void tick_nohz_enable(void) { }
+static inline void tick_nohz_disable(int wakeup) { }
# endif /* !NO_HZ */

#endif
diff -urpN linux-2.6/kernel/profile.c linux-2.6-patched/kernel/profile.c
--- linux-2.6/kernel/profile.c 2009-06-22 11:26:26.000000000 +0200
+++ linux-2.6-patched/kernel/profile.c 2009-06-22 11:26:50.000000000 +0200
@@ -24,6 +24,7 @@
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
+#include <linux/tick.h>
#include <asm/sections.h>
#include <asm/irq_regs.h>
#include <asm/ptrace.h>
@@ -97,6 +98,8 @@ int profile_setup(char *str)
printk(KERN_INFO "kernel profiling enabled (shift: %ld)\n",
prof_shift);
}
+ if (prof_on)
+ tick_nohz_disable(0);
return 1;
}
__setup("profile=", profile_setup);
@@ -582,6 +585,7 @@ static int create_hash_tables(void)
return 0;
out_cleanup:
prof_on = 0;
+ tick_nohz_enable();
smp_mb();
on_each_cpu(profile_nop, NULL, 1);
for_each_online_cpu(cpu) {
diff -urpN linux-2.6/kernel/time/tick-sched.c linux-2.6-patched/kernel/time/tick-sched.c
--- linux-2.6/kernel/time/tick-sched.c 2009-06-22 11:26:26.000000000 +0200
+++ linux-2.6-patched/kernel/time/tick-sched.c 2009-06-22 11:26:50.000000000 +0200
@@ -124,6 +124,30 @@ static int __init setup_tick_nohz(char *

__setup("nohz=", setup_tick_nohz);

+/*
+ * NO HZ currently disabled ?
+ */
+static atomic_t tick_nohz_disable_counter = ATOMIC_INIT(0);
+
+void tick_nohz_enable(void)
+{
+ atomic_dec(&tick_nohz_disable_counter);
+}
+EXPORT_SYMBOL_GPL(tick_nohz_enable);
+
+static void __tick_nohz_disable(void *dummy)
+{
+}
+
+void tick_nohz_disable(int wakeup)
+{
+ if (atomic_inc_return(&tick_nohz_disable_counter) == 1)
+ if (wakeup)
+ /* Wake up all cpus to make them start ticking. */
+ smp_call_function(__tick_nohz_disable, NULL, 0);
+}
+EXPORT_SYMBOL_GPL(tick_nohz_disable);
+
/**
* tick_nohz_update_jiffies - update jiffies when idle was interrupted
*
@@ -276,7 +300,8 @@ void tick_nohz_stop_sched_tick(int inidl
next_jiffies = get_next_timer_interrupt(last_jiffies);
delta_jiffies = next_jiffies - last_jiffies;

- if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu))
+ if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
+ atomic_read(&tick_nohz_disable_counter) > 0)
delta_jiffies = 1;
/*
* Do not stop the tick, if we are only one off