On 04/10/2013 11:30 AM, Michael Wang wrote:
Now long time has been passed since the first version, I'd like to
do some summary about current states:
On a 12 cpu box with tip 3.9.0-rc7, test show that:
1. remove wake-affine stuff cause regression on hackbench (could be 15%).
2. reserve wake-affine stuff cause regression on pgbench (could be 45%).
And since neither remove or reserve is acceptable, this patch introduced a
knob to throttle wake-affine stuff.
By turning the knob, we could benefit both hackbench and pgbench, or sacrifice
one to significantly benefit another.
All similar workload which prefer or hate wake-affine behaviour could
been cared.
If this approach caused any concerns, please let me know ;-)
Regards,
Michael Wang
>
> 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.
>
> 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.zijls...@chello.nl>
> Signed-off-by: Michael Wang <wang...@linux.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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