Re: [PATCH V2 2/3] timer: hrtimer: Don't check idle_cpu() beforecalling get_nohz_timer_target()

[Viresh Kumar]

On 27 September 2012 14:34, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:

>  #if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
> -       if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
> +       if (!pinned && get_sysctl_timer_migration())
>                 cpu = get_nohz_timer_target();
>  #endif
> +       if (!cpu)
> +               cpu = smp_processor_id();

Ahh... Bad change... cpu can be returned as zero by get_nohz_timer_target().

Please consider below patch here:

------------8<-------------


Subject: [PATCH] timer: hrtimer: Don't check idle_cpu() before calling
 get_nohz_timer_target()

Check for current cpu's idleness already done in implementation of
sched_select_cpu() which is called by get_nohz_timer_target(). So, no need to
call idle_cpu() twice, once from sched_select_cpu() and once from timer and
hrtimer before calling get_nohz_timer_target().

This patch removes calls to idle_cpu() from timer and hrtimer.

This also reduces an extra call to smp_processor_id() when
get_nohz_timer_target() is called.

Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
 kernel/hrtimer.c | 2 +-
 kernel/timer.c   | 8 +++++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 6db7a5e..74bdaf6 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -159,7 +159,7 @@ struct hrtimer_clock_base *lock_hrtimer_base(const
struct hrtimer *timer,
 static int hrtimer_get_target(int this_cpu, int pinned)
 {
 #ifdef CONFIG_NO_HZ
-	if (!pinned && get_sysctl_timer_migration() && idle_cpu(this_cpu))
+	if (!pinned && get_sysctl_timer_migration())
 		return get_nohz_timer_target();
 #endif
 	return this_cpu;
diff --git a/kernel/timer.c b/kernel/timer.c
index d5de1b2..db57606 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -733,11 +733,13 @@ __mod_timer(struct timer_list *timer, unsigned
long expires,

 	debug_activate(timer, expires);

-	cpu = smp_processor_id();
-
 #if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
-	if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
+	if (!pinned && get_sysctl_timer_migration())
 		cpu = get_nohz_timer_target();
+	else
+		cpu = smp_processor_id();
+#else
+	cpu = smp_processor_id();
 #endif
 	new_base = per_cpu(tvec_bases, cpu);
--
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