[PATCH] trace: stop critical timings before idle loop on idle=poll

[PATCH] trace: stop critical timings before idle loop on idle=poll

[Daniel Bristot de Oliveira]

When using idle=poll, the preemptoff tracer is always showing the idle
task as the culprit for long latencies. That happens because critical
timings are not stopped before idle loop. This patch stops critical
timings before entering the idle loop, starting it again after the
idle loop.

This problem does not affect the irqsoff tracer because interruptions
are enabled before entering the idle loop.

Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Reviewed-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
---
 kernel/sched/idle.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 8f177c7..4a2ef5a 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -57,9 +57,11 @@ static inline int cpu_idle_poll(void)
 	rcu_idle_enter();
 	trace_cpu_idle_rcuidle(0, smp_processor_id());
 	local_irq_enable();
+	stop_critical_timings();
 	while (!tif_need_resched() &&
 		(cpu_idle_force_poll || tick_check_broadcast_expired()))
 		cpu_relax();
+	start_critical_timings();
 	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
 	rcu_idle_exit();
 	return 1;
-- 
2.4.3

Re: [PATCH] trace: stop critical timings before idle loop on idle=poll

[Steven Rostedt]

On Thu,  8 Oct 2015 15:36:06 -0300
Daniel Bristot de Oliveira <bristot@redhat.com> wrote:

> When using idle=poll, the preemptoff tracer is always showing the idle
> task as the culprit for long latencies. That happens because critical
> timings are not stopped before idle loop. This patch stops critical
> timings before entering the idle loop, starting it again after the
> idle loop.
> 
> This problem does not affect the irqsoff tracer because interruptions
> are enabled before entering the idle loop.
> 
> Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
> Reviewed-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>

Acked-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve

> ---
>  kernel/sched/idle.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 8f177c7..4a2ef5a 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -57,9 +57,11 @@ static inline int cpu_idle_poll(void)
>  	rcu_idle_enter();
>  	trace_cpu_idle_rcuidle(0, smp_processor_id());
>  	local_irq_enable();
> +	stop_critical_timings();
>  	while (!tif_need_resched() &&
>  		(cpu_idle_force_poll || tick_check_broadcast_expired()))
>  		cpu_relax();
> +	start_critical_timings();
>  	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
>  	rcu_idle_exit();
>  	return 1;

[tip:sched/urgent] sched, tracing: Stop/ start critical timings around the idle=poll idle loop

[tip-bot for Daniel Bristot de Oliveira]

Commit-ID:  9babcd7929bc8967ae3bb6093f603b93c2f9958f
Gitweb:     http://git.kernel.org/tip/9babcd7929bc8967ae3bb6093f603b93c2f9958f
Author:     Daniel Bristot de Oliveira <bristot@redhat.com>
AuthorDate: Thu, 8 Oct 2015 15:36:06 -0300
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 12 Oct 2015 09:45:25 +0200

sched, tracing: Stop/start critical timings around the idle=poll idle loop

When using idle=poll, the preemptoff tracer is always showing
the idle task as the culprit for long latencies. That happens
because critical timings are not stopped before idle loop. This
patch stops critical timings before entering the idle loop,
starting it again after the idle loop.

This problem does not affect the irqsoff tracer because
interruptions are enabled before entering the idle loop.

Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Reviewed-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/10fc3705874aef11dbe152a068b591a7be1899b4.1444314899.git.bristot@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/idle.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 8f177c7..4a2ef5a 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -57,9 +57,11 @@ static inline int cpu_idle_poll(void)
 	rcu_idle_enter();
 	trace_cpu_idle_rcuidle(0, smp_processor_id());
 	local_irq_enable();
+	stop_critical_timings();
 	while (!tif_need_resched() &&
 		(cpu_idle_force_poll || tick_check_broadcast_expired()))
 		cpu_relax();
+	start_critical_timings();
 	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
 	rcu_idle_exit();
 	return 1;