Re: Reporting a performance regression in sched/fair on Unixbench Shell Scripts with commit a53ce18cacb4

From: Vincent Guittot
Date: Fri Jul 21 2023 - 10:01:39 EST

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In reply to: Saeed Mirzamohammadi: "Re: Reporting a performance regression in sched/fair on Unixbench Shell Scripts with commit a53ce18cacb4"
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Hi Saeed,

On Fri, 21 Jul 2023 at 01:04, Saeed Mirzamohammadi
<saeed.mirzamohammadi@xxxxxxxxxx> wrote:
>
> Hi Vincent,
>
> > On Jun 30, 2023, at 1:28 AM, Vincent Guittot <vincent.guittot@xxxxxxxxxx> wrote:
> >
> > On Fri, 30 Jun 2023 at 00:20, Saeed Mirzamohammadi
> > <saeed.mirzamohammadi@xxxxxxxxxx> wrote:
> >>
> >>
> >>
> >>> On Jun 21, 2023, at 9:41 AM, Saeed Mirzamohammadi <saeed.mirzamohammadi@xxxxxxxxxx> wrote:
> >>>
> >>> Hi Chen, Vincent,
> >>>
> >>>> On Jun 13, 2023, at 11:37 PM, Chen Yu <yu.c.chen@xxxxxxxxx> wrote:
> >>>>
> >>>> On 2023-06-13 at 19:35:55 +0000, Saeed Mirzamohammadi wrote:
> >>>>> Hi Vincent,
> >>>>>
> >>>>>> On Jun 9, 2023, at 9:52 AM, Vincent Guittot <vincent.guittot@xxxxxxxxxx> wrote:
> >>>>>>
> >>>>>> Hi Saeed,
> >>>>>>
> >>>>>> On Fri, 9 Jun 2023 at 00:48, Saeed Mirzamohammadi
> >>>>>> <saeed.mirzamohammadi@xxxxxxxxxx> wrote:
> >>>>>>>
> >>>>>>> Hi all,
> >>>>>>>
> >>>>>>> I’m reporting a regression of up to 8% with Unixbench Shell Scripts benchmarks after the following commit:
> >>>>>>>
> >>>>>>> Commit Data:
> >>>>>>> commit-id : a53ce18cacb477dd0513c607f187d16f0fa96f71
> >>>>>>> subject : sched/fair: Sanitize vruntime of entity being migrated
> >>>>>>> author : vincent.guittot@xxxxxxxxxx
> >>>>>>> author date : 2023-03-17 16:08:10
> >>>>>>>
> >>>>>>>
> >>>>>>> We have observed this on our v5.4 and v4.14 kernel and not yet tested 5.15 but I expect the same.
> >>>>>>
> >>>>>> It would be good to confirm that the regression is present on v6.3
> >>>>>> where the patch has been merged originally. It can be that there is
> >>>>>> hidden dependency with other patches introduced since v5.4
> >>>>>
> >>>>> Regression is present on v6.3 as well, examples:
> >>>>> ub_gcc_224copies_Shell_Scripts_8_concurrent: ~6%
> >>>>> ub_gcc_224copies_Shell_Scripts_16_concurrent: ~8%
> >>>>> ub_gcc_448copies_Shell_Scripts_1_concurrent: ~2%
> >>>
> >>> Apologize for the confusion, I should correct the v6.3 upstream result above. v6.3 doesn’t have any regression.
> >>> v6.3.y -> no regression
> >>> v5.15.y -> no regression
> >>> v5.4.y -> 5-8% regression.
> >>
> >> A gentle reminder if there is any recommendation for v5.4.y and v4.14.y regression. Thanks!
> >
> > I tried to find why the regression happens only for v5.4.y (or lower)
> > and not for v5.15.y (or above) but I haven't been able to find any
> > possible reason in the code.
> >
> > Regarding the 2 commits below, they must come together so we can't
> > simply revert 1 and not the other.
> > commit 829c1651e9c4 sched/fair: sanitize vruntime of entity being placed
> > commit a53ce18cacb4 sched/fair: Sanitize vruntime of entity being migrated
> >
> Tests were done before and after these 2 commits.
>
> > entity_is_long_sleeper() should never return true in your case. Could
> > you try to check that it's the case for you ?
> >
> Tested this and entity_is_long_sleeper() never returns True.
>
> I actually removed the related part, tested, and the regression is gone with the following change (partial revert):
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3ebd2054996bc..0d70dd6e14844 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -792,9 +792,6 @@ static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
>
> void activate_task(struct rq *rq, struct task_struct *p, int flags)
> {
> - if (task_on_rq_migrating(p))
> - flags |= ENQUEUE_MIGRATED;
> -
> if (task_contributes_to_load(p))
> rq->nr_uninterruptible--;
>

Is the regression still there if you only apply the partial revert
below but not the above part ?
I have rechecked the code but can't see any obvious reason why there
is a regression on v5.4 and not on v5.15.

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 83a7cf62c0f53..ef9aca05c7bdf 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3779,9 +3779,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>
> if (flags & ENQUEUE_WAKEUP)
> place_entity(cfs_rq, se, 0);
> - /* Entity has migrated, no longer consider this task hot */
> - if (flags & ENQUEUE_MIGRATED)
> - se->exec_start = 0;
>
> check_schedstat_required();
> update_stats_enqueue(cfs_rq, se, flags);
> @@ -6182,6 +6179,9 @@ static void migrate_task_rq_fair(struct task_struct *p)
>
> /* Tell new CPU we are migrated */
> p->se.avg.last_update_time = 0;
> +
> + /* We have migrated, no longer consider this task hot */
> + p->se.exec_start = 0;
> }
>
> static void task_dead_fair(struct task_struct *p)
>
>
> >
> >
> >
> >
> >>
> >>>
> >>>
> >>>>>>
> >>>>>>
> >>>>>>>
> >>>>>>> ub_gcc_1copy_Shell_Scripts_1_concurrent : -0.01%
> >>>>>>> ub_gcc_1copy_Shell_Scripts_8_concurrent : -0.1%
> >>>>>>> ub_gcc_1copy_Shell_Scripts_16_concurrent : -0.12%%
> >>>>>>> ub_gcc_56copies_Shell_Scripts_1_concurrent : -2.29%%
> >>>>>>> ub_gcc_56copies_Shell_Scripts_8_concurrent : -4.22%
> >>>>>>> ub_gcc_56copies_Shell_Scripts_16_concurrent : -4.23%
> >>>>>>> ub_gcc_224copies_Shell_Scripts_1_concurrent : -5.54%
> >>>>>>> ub_gcc_224copies_Shell_Scripts_8_concurrent : -8%
> >>>>>>> ub_gcc_224copies_Shell_Scripts_16_concurrent : -7.05%
> >>>>>>> ub_gcc_448copies_Shell_Scripts_1_concurrent : -6.4%
> >>>>>>> ub_gcc_448copies_Shell_Scripts_8_concurrent : -8.35%
> >>>>>>> ub_gcc_448copies_Shell_Scripts_16_concurrent : -7.09%
> >>>>>>>
> >>>>>>> Link to unixbench:
> >>>>>>> github.com/kdlucas/byte-unixbench
> >>>>>>
> >>>>>> I tried to reproduce the problem with v6.3 on my system but I don't
> >>>>>> see any difference with or without the patch
> >>>>>>
> >>>>>> Do you have more details on your setup ? number of cpu and topology ?
> >>>>>>
> >>>>> model name : Intel(R) Xeon(R) CPU E5-2690 v4 @ 2.60GHz
> >>>>>
> >>>>> Topology:
> >>>>> node 0 1
> >>>>> 0: 10 21
> >>>>> 1: 21 10
> >>>>>
> >>>>> Architecture: x86_64
> >>>>> CPU op-mode(s): 32-bit, 64-bit
> >>>>> CPU(s): 56
> >>>>> On-line CPU(s) list: 0-55
> >>>>> Thread(s) per core: 2
> >>>>> Core(s) per socket: 14
> >>>>> Socket(s): 2
> >>>>> NUMA node(s): 2
> >>>>>
> >>>> Tested on a similar platform E5-2697 v2 @ 2.70GHz which has 2 nodes,
> >>>> 24 cores/48 CPUs in total, however I could not reproduce the issue.
> >>>> Since the regression was reported mainly against 224 and 448 copies case
> >>>> on your platform, I tested unixbench shell1 with 4 x 48 = 192 copies.
> >>>>
> >>>>
> >>>> a53ce18cacb477dd 213acadd21a080fc8cda8eebe6d
> >>>> ---------------- ---------------------------
> >>>> %stddev %change %stddev
> >>>> \ | \
> >>>> 21304 +0.5% 21420 unixbench.score
> >>>> 632.43 +0.0% 632.44 unixbench.time.elapsed_time
> >>>> 632.43 +0.0% 632.44 unixbench.time.elapsed_time.max
> >>>> 11837046 -4.7% 11277727 unixbench.time.involuntary_context_switches
> >>>> 864713 +0.1% 865914 unixbench.time.major_page_faults
> >>>> 9600 +4.0% 9984 unixbench.time.maximum_resident_set_size
> >>>> 8.433e+08 +0.6% 8.48e+08 unixbench.time.minor_page_faults
> >>>> 4096 +0.0% 4096 unixbench.time.page_size
> >>>> 3741 +1.1% 3783 unixbench.time.percent_of_cpu_this_job_got
> >>>> 18341 +1.3% 18572 unixbench.time.system_time
> >>>> 5323 +0.6% 5353 unixbench.time.user_time
> >>>> 78197044 -3.1% 75791701 unixbench.time.voluntary_context_switches
> >>>> 57178573 +0.4% 57399061 unixbench.workload
> >>>>
> >>>> There is no much difference with a53ce18cacb477dd applied or not.
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>> a2e90611b9f425ad 829c1651e9c4a6f78398d3e6765
> >>>> ---------------- ---------------------------
> >>>> %stddev %change %stddev
> >>>> \ | \
> >>>> 19985 +8.6% 21697 unixbench.score
> >>>> 632.64 -0.0% 632.53 unixbench.time.elapsed_time
> >>>> 632.64 -0.0% 632.53 unixbench.time.elapsed_time.max
> >>>> 11453985 +3.7% 11880259 unixbench.time.involuntary_context_switches
> >>>> 818996 +3.1% 844681 unixbench.time.major_page_faults
> >>>> 9600 +0.0% 9600 unixbench.time.maximum_resident_set_size
> >>>> 7.911e+08 +8.4% 8.575e+08 unixbench.time.minor_page_faults
> >>>> 4096 +0.0% 4096 unixbench.time.page_size
> >>>> 3767 -0.4% 3752 unixbench.time.percent_of_cpu_this_job_got
> >>>> 18873 -2.4% 18423 unixbench.time.system_time
> >>>> 4960 +7.1% 5313 unixbench.time.user_time
> >>>> 75436000 +10.8% 83581483 unixbench.time.voluntary_context_switches
> >>>> 53553404 +8.7% 58235303 unixbench.workload
> >>>>
> >>>> Previously with 829c1651e9c4a6f introduced, there is 8.6% improvement. And this improvement
> >>>> remains with a53ce18cacb477dd applied.
> >>>>
> >>>> Can you send the full test script so I can have a try locally?
> >>>
> >>> Thanks for testing this. For v5.4.y kernel (not for v6.3.y or v5.15.y), there is an 8% regression with the following test: ub_gcc_448copies_Shell_Scripts_8_concurrent
> >>> And that’s ’shell8’ with ‘-c 448’ copies passed as argument.
> >>>
> >>> Thanks,
> >>> Saeed
> >>>
> >>>>
> >>>> thanks,
> >>>> Chenyu
>

Next message: Krzysztof Kozlowski: "Re: [PATCH v3 04/42] dt-bindings: pinctrl: Add Cirrus EP93xx"
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In reply to: Saeed Mirzamohammadi: "Re: Reporting a performance regression in sched/fair on Unixbench Shell Scripts with commit a53ce18cacb4"
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