On 27 September 2012 14:34, Viresh Kumar viresh.kumar@linaro.org 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@linaro.org --- 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);