On 05/03/2013 11:46 AM, Michael Wang wrote:
> 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 ;-)
Is there any more concerns? or should we take some action now?
Regards,
Michael Wang
>
> 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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