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Date: Mon, 22 Apr 2013 07:27:03 +0200
From: Mike Galbraith <efault@....de>
To: Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Peter Zijlstra <peterz@...radead.org>,
Alex Shi <alex.shi@...el.com>,
Namhyung Kim <namhyung@...nel.org>,
Paul Turner <pjt@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
Ram Pai <linuxram@...ibm.com>
Subject: Re: [PATCH] sched: wake-affine throttle
On Mon, 2013-04-22 at 12:21 +0800, Michael Wang wrote:
> On 04/10/2013 11:30 AM, Michael Wang wrote:
> > Log since RFC:
> > 1. Throttle only when wake-affine failed. (thanks to PeterZ)
> > 2. Do throttle inside wake_affine(). (thanks to PeterZ)
> > 3. Other small fix.
> >
> > Recently testing show that wake-affine stuff cause regression on pgbench, the
> > hiding rat was finally catched out.
> >
> > wake-affine stuff is always trying to pull wakee close to waker, by theory,
> > this will benefit us if waker's cpu cached hot data for wakee, or the extreme
> > ping-pong case.
> >
> > However, the whole stuff is somewhat blindly, load balance is the only factor
> > to be guaranteed, and since the stuff itself is time-consuming, some workload
> > suffered, pgbench is just the one who has been found.
> >
> > Thus, throttle the wake-affine stuff for such workload is necessary.
> >
> > This patch introduced a new knob 'sysctl_sched_wake_affine_interval' with the
> > default value 1ms (default minimum balance interval), which means wake-affine
> > will keep silent for 1ms after it returned false.
> >
> > By turning the new knob, those workload who suffered will have the chance to
> > stop the regression.
>
> I have tested the latest tip 3.9.0-rc7, huge regression on pgbench is
> still there and this approach still works well, should we take the
> action now?
(It's not a _regression_ per se, more of a long standing issue for this
sort of load. Not that the load cares much what we call the problem;)
>
> Regards,
> Michael Wang
>
> >
> > Test:
> > Test with 12 cpu X86 server and tip 3.9.0-rc2.
> >
> > default
> > base 1ms interval 10ms interval 100ms interval
> > | db_size | clients | tps | | tps | | tps | | tps |
> > +---------+---------+-------+- +-------+ +-------+ +-------+
> > | 21 MB | 1 | 10572 | | 10804 | | 10802 | | 10801 |
> > | 21 MB | 2 | 21275 | | 21533 | | 21400 | | 21498 |
> > | 21 MB | 4 | 41866 | | 42158 | | 42410 | | 42306 |
> > | 21 MB | 8 | 53931 | | 55796 | | 58608 | +8.67% | 59916 | +11.10%
> > | 21 MB | 12 | 50956 | | 52266 | | 54586 | +7.12% | 55982 | +9.86%
> > | 21 MB | 16 | 49911 | | 52862 | +5.91% | 55668 | +11.53% | 57255 | +14.71%
> > | 21 MB | 24 | 46046 | | 48820 | +6.02% | 54269 | +17.86% | 58113 | +26.21%
> > | 21 MB | 32 | 43405 | | 46635 | +7.44% | 53690 | +23.70% | 57729 | +33.00%
> > | 7483 MB | 1 | 7734 | | 8013 | | 8046 | | 7879 |
> > | 7483 MB | 2 | 19375 | | 19459 | | 19448 | | 19421 |
> > | 7483 MB | 4 | 37408 | | 37780 | | 37937 | | 37819 |
> > | 7483 MB | 8 | 49033 | | 50389 | | 51636 | +5.31% | 52294 | +6.65%
> > | 7483 MB | 12 | 45525 | | 47794 | +4.98% | 49828 | +9.45% | 50571 | +11.08%
> > | 7483 MB | 16 | 45731 | | 47921 | +4.79% | 50203 | +9.78% | 52033 | +13.78%
> > | 7483 MB | 24 | 41533 | | 44301 | +6.67% | 49697 | +19.66% | 53833 | +29.62%
> > | 7483 MB | 32 | 36370 | | 38301 | +5.31% | 48146 | +32.38% | 52795 | +45.16%
> > | 15 GB | 1 | 7576 | | 7926 | | 7722 | | 7969 |
> > | 15 GB | 2 | 19157 | | 19284 | | 19294 | | 19304 |
> > | 15 GB | 4 | 37285 | | 37539 | | 37281 | | 37508 |
> > | 15 GB | 8 | 48718 | | 49176 | | 50836 | +4.35% | 51239 | +5.17%
> > | 15 GB | 12 | 45167 | | 47180 | +4.45% | 49206 | +8.94% | 50126 | +10.98%
> > | 15 GB | 16 | 45270 | | 47293 | +4.47% | 49638 | +9.65% | 51748 | +14.31%
> > | 15 GB | 24 | 40984 | | 43366 | +5.81% | 49356 | +20.43% | 53157 | +29.70%
> > | 15 GB | 32 | 35918 | | 37632 | +4.77% | 47923 | +33.42% | 52241 | +45.45%
> >
> > Suggested-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Signed-off-by: Michael Wang <wangyun@...ux.vnet.ibm.com>
> > ---
> > include/linux/sched.h | 5 +++++
> > kernel/sched/fair.c | 31 +++++++++++++++++++++++++++++++
> > kernel/sysctl.c | 10 ++++++++++
> > 3 files changed, 46 insertions(+), 0 deletions(-)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index d35d2b6..e9efd3a 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1197,6 +1197,10 @@ enum perf_event_task_context {
> > perf_nr_task_contexts,
> > };
> >
> > +#ifdef CONFIG_SMP
> > +extern unsigned int sysctl_sched_wake_affine_interval;
> > +#endif
> > +
> > struct task_struct {
> > volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */
> > void *stack;
> > @@ -1207,6 +1211,7 @@ struct task_struct {
> > #ifdef CONFIG_SMP
> > struct llist_node wake_entry;
> > int on_cpu;
> > + unsigned long next_wake_affine;
> > #endif
> > int on_rq;
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 7a33e59..68eedd7 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3087,6 +3087,22 @@ static inline unsigned long effective_load(struct task_group *tg, int cpu,
> >
> > #endif
> >
> > +/*
> > + * Default is 1ms, to prevent the wake_affine() stuff working too frequently.
> > + */
> > +unsigned int sysctl_sched_wake_affine_interval = 1U;
> > +
> > +static inline int wake_affine_throttled(struct task_struct *p)
> > +{
> > + return time_before(jiffies, p->next_wake_affine);
> > +}
> > +
> > +static inline void wake_affine_throttle(struct task_struct *p)
> > +{
> > + p->next_wake_affine = jiffies +
> > + msecs_to_jiffies(sysctl_sched_wake_affine_interval);
> > +}
> > +
> > static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
> > {
> > s64 this_load, load;
> > @@ -3096,6 +3112,9 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
> > unsigned long weight;
> > int balanced;
> >
> > + if (wake_affine_throttled(p))
> > + return 0;
> > +
> > idx = sd->wake_idx;
> > this_cpu = smp_processor_id();
> > prev_cpu = task_cpu(p);
> > @@ -3167,6 +3186,18 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
> >
> > return 1;
> > }
> > +
> > + /*
> > + * wake_affine() stuff try to pull wakee to the cpu
> > + * around waker, this will benefit us if the data
> > + * cached on waker cpu is hot for wakee, or the extreme
> > + * ping-pong case.
> > + *
> > + * However, do such blindly work too frequently will
> > + * cause regression to some workload, thus, each time
> > + * when wake_affine() failed, throttle it for a while.
> > + */
> > + wake_affine_throttle(p);
> > return 0;
> > }
> >
> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > index afc1dc6..6ebfc18 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -437,6 +437,16 @@ static struct ctl_table kern_table[] = {
> > .extra1 = &one,
> > },
> > #endif
> > +#ifdef CONFIG_SMP
> > + {
> > + .procname = "sched_wake_affine_interval",
> > + .data = &sysctl_sched_wake_affine_interval,
> > + .maxlen = sizeof(unsigned int),
> > + .mode = 0644,
> > + .proc_handler = proc_dointvec_minmax,
> > + .extra1 = &zero,
> > + },
> > +#endif
> > #ifdef CONFIG_PROVE_LOCKING
> > {
> > .procname = "prove_locking",
> >
>
--
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