Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 21 Jul 2023 16:01:20 +0200 | Subject | 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@oracle.com> wrote: > > Hi Vincent, > > > On Jun 30, 2023, at 1:28 AM, Vincent Guittot <vincent.guittot@linaro.org> wrote: > > > > On Fri, 30 Jun 2023 at 00:20, Saeed Mirzamohammadi > > <saeed.mirzamohammadi@oracle.com> wrote: > >> > >> > >> > >>> On Jun 21, 2023, at 9:41 AM, Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com> wrote: > >>> > >>> Hi Chen, Vincent, > >>> > >>>> On Jun 13, 2023, at 11:37 PM, Chen Yu <yu.c.chen@intel.com> 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@linaro.org> wrote: > >>>>>> > >>>>>> Hi Saeed, > >>>>>> > >>>>>> On Fri, 9 Jun 2023 at 00:48, Saeed Mirzamohammadi > >>>>>> <saeed.mirzamohammadi@oracle.com> 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@linaro.org > >>>>>>> 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 >
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