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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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