Messages in this thread | | | Subject | Re: [patch 3/6] sched: use rq->avg_event to resurrect nohz ratelimiting | From | Peter Zijlstra <> | Date | Fri, 18 Nov 2011 16:36:59 +0100 |
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On Fri, 2011-11-18 at 16:19 +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>
Arjan, can we do something smart with the idle governor which already guestimates the idle duration for us?
> --- > include/linux/sched.h | 2 ++ > kernel/sched.c | 7 +++++++ > kernel/time/tick-sched.c | 2 +- > 3 files changed, 10 insertions(+), 1 deletion(-) > > Index: linux-3.2.git/include/linux/sched.h > =================================================================== > --- linux-3.2.git.orig/include/linux/sched.h > +++ linux-3.2.git/include/linux/sched.h > @@ -1979,8 +1979,10 @@ 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-3.2.git/kernel/sched.c > =================================================================== > --- linux-3.2.git.orig/kernel/sched.c > +++ linux-3.2.git/kernel/sched.c > @@ -1419,6 +1419,13 @@ 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-3.2.git/kernel/time/tick-sched.c > =================================================================== > --- linux-3.2.git.orig/kernel/time/tick-sched.c > +++ linux-3.2.git/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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