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SubjectRe: [patch 6/7] sched: use rq->avg_event to resurrect nohz ratelimiting
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Added CC of the person who reported that the last nohz ratelimit patch
caused increased power consumption.

Norbert: can you please test this patch to make sure it's not going to
cause you the same trouble the last one did? I see no ill effects with
this patch, but then I didn't with the last either.

TIA,

-Mike

On Tue, 2011-11-22 at 15:24 +0100, Mike Galbraith wrote:
> Entering nohz at high frequency eats cycles, ratelimit it
> just as we do idle_balance(), and for the same reason.
>
> Signed-off-by: Mike Galbraith <efault@gmx.de>
>
> ---
> include/linux/sched.h | 2 ++
> kernel/sched/core.c | 7 +++++++
> kernel/time/tick-sched.c | 2 +-
> 3 files changed, 10 insertions(+), 1 deletion(-)
>
> Index: linux-3.0-tip/include/linux/sched.h
> ===================================================================
> --- linux-3.0-tip.orig/include/linux/sched.h
> +++ linux-3.0-tip/include/linux/sched.h
> @@ -1988,8 +1988,10 @@ static inline void idle_task_exit(void)
>
> #if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
> extern void wake_up_idle_cpu(int cpu);
> +extern int sched_needs_cpu(int cpu);
> #else
> static inline void wake_up_idle_cpu(int cpu) { }
> +static inline void sched_needs_cpu(int cpu) { }
> #endif
>
> extern unsigned int sysctl_sched_latency;
> Index: linux-3.0-tip/kernel/sched/core.c
> ===================================================================
> --- linux-3.0-tip.orig/kernel/sched/core.c
> +++ linux-3.0-tip/kernel/sched/core.c
> @@ -587,6 +587,13 @@ static inline bool got_nohz_idle_kick(vo
> return idle_cpu(smp_processor_id()) && this_rq()->nohz_balance_kick;
> }
>
> +#ifdef CONFIG_SMP
> +int sched_needs_cpu(int cpu)
> +{
> + return cpu_rq(cpu)->avg_event < sysctl_sched_migration_cost;
> +}
> +#endif
> +
> #else /* CONFIG_NO_HZ */
>
> static inline bool got_nohz_idle_kick(void)
> Index: linux-3.0-tip/kernel/time/tick-sched.c
> ===================================================================
> --- linux-3.0-tip.orig/kernel/time/tick-sched.c
> +++ linux-3.0-tip/kernel/time/tick-sched.c
> @@ -352,7 +352,7 @@ void tick_nohz_stop_sched_tick(int inidl
> } while (read_seqretry(&xtime_lock, seq));
>
> if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
> - arch_needs_cpu(cpu)) {
> + arch_needs_cpu(cpu) || sched_needs_cpu(cpu)) {
> next_jiffies = last_jiffies + 1;
> delta_jiffies = 1;
> } else {
>
>




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