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Date: Fri, 10 Jul 2020 14:48:32 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Tao Zhou <ouwen210@...mail.com>
Cc: Xing Zhengjun <zhengjun.xing@...ux.intel.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
Hillf Danton <hdanton@...a.com>,
kernel test robot <rong.a.chen@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Mel Gorman <mgorman@...e.de>
Subject: Re: [LKP] [sched/fair] 6c8116c914: stress-ng.mmapfork.ops_per_sec
-38.0% regression
On Fri, 10 Jul 2020 at 14:08, Tao Zhou <ouwen210@...mail.com> wrote:
>
> Hi Vincent,
>
> Sorry for this so late reply.
>
> On Tue, Jun 30, 2020 at 04:22:10PM +0200, Vincent Guittot wrote:
> > Hi Tao,
> >
> > On Tue, 30 Jun 2020 at 11:41, Tao Zhou <ouwen210@...mail.com> wrote:
> > >
> > > Hi,
> > >
> > > On Tue, Jun 30, 2020 at 09:43:11AM +0200, Vincent Guittot wrote:
> > > > Hi Tao,
> > > >
> > > > Le lundi 15 juin 2020 à 16:14:01 (+0800), Xing Zhengjun a écrit :
> > > > >
> > > > >
> > > > > On 6/15/2020 1:18 PM, Tao Zhou wrote:
> > > >
> > > > ...
> > > >
> > > > > I apply the patch based on v5.7, the regression still existed.
> > > >
> > > >
> > > > Could you try the patch below ? This patch is not a real fix because it impacts performance of others benchmarks but it will at least narrow your problem.
> > > >
> > > >
> > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > > index 9f78eb76f6fb..a4d8614b1854 100644
> > > > --- a/kernel/sched/fair.c
> > > > +++ b/kernel/sched/fair.c
> > > > @@ -8915,9 +8915,9 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
> > > > * and consider staying local.
> > > > */
> > > >
> > > > - if ((sd->flags & SD_NUMA) &&
> > > > - ((idlest_sgs.avg_load + imbalance) >= local_sgs.avg_load))
> > > > - return NULL;
> > > > +// if ((sd->flags & SD_NUMA) &&
> > > > +// ((idlest_sgs.avg_load + imbalance) >= local_sgs.avg_load))
> > > > +// return NULL;
> > >
> > > Just narrow to the fork (wakeup) path that maybe lead the problem, /me think.
> >
> > The perf regression seems to be fixed with this patch on my setup.
> > According to the statistics that I have on the use case, groups are
> > overloaded but load is quite low and this low level hits this NUMA
> > specific condition
>
> My box has 1 Socket, 4 Core, 2 Threads per core and 2x4 CPUS.
> (x86_64 Intel(R) Core(TM) i7-6700HQ)
The change above only applies to NUMA system which doesn't seems to be
the case for your setup
>
> stress-ng.mmapfork
>
> v5.8-rc4:
>
> stress-ng: info: [7158] dispatching hogs: 8 mmapfork
> stress-ng: info: [7158] successful run completed in 1.09s
> stress-ng: info: [7158] stressor bogo ops real time usr time sys time bogo ops/s bogo ops/s
> stress-ng: info: [7158] (secs) (secs) (secs) (real time) (usr+sys time)
> stress-ng: info: [7158] mmapfork 32 1.09 2.48 6.01 29.36 3.77
> stress-ng: info: [7158] for a 1.09s run time:
> stress-ng: info: [7158] 8.73s available CPU time
> stress-ng: info: [7158] 2.52s user time ( 28.86%)
> stress-ng: info: [7158] 6.07s system time ( 69.52%)
> stress-ng: info: [7158] 8.59s total time ( 98.38%)
> stress-ng: info: [7158] load average: 0.52 0.26 0.10
>
> v5.8-rc4 w/ above patch:
>
> stress-ng: info: [5126] dispatching hogs: 8 mmapfork
> stress-ng: info: [5126] successful run completed in 1.07s
> stress-ng: info: [5126] stressor bogo ops real time usr time sys time bogo ops/s bogo ops/s
> stress-ng: info: [5126] (secs) (secs) (secs) (real time) (usr+sys time)
> stress-ng: info: [5126] mmapfork 32 1.07 2.45 5.96 29.88 3.80
> stress-ng: info: [5126] for a 1.07s run time:
> stress-ng: info: [5126] 8.58s available CPU time
> stress-ng: info: [5126] 2.49s user time ( 29.02%)
> stress-ng: info: [5126] 6.02s system time ( 70.17%)
> stress-ng: info: [5126] 8.51s total time ( 99.19%)
> stress-ng: info: [5126] load average: 0.31 0.22 0.09
>
> No obvious changes.
Yeah, the problem happens for system with several numa nodes
>
> And I traced and also tried to find the task_h_load = 0 after the patch you sent.
>
> I used the command:
>
> trace-cmd record -e sched -e irq -e cpu_idle -e cpu_frequency -e timer cgexec -g cpu:A\
> stress-ng --timeout 1 --times --verify--metrics-brief --sequential 8 --class scheduler\
> --exclude (all exclude but mmapfork)
>
> <...>-26132 [000] 6571.361156: bprint: task_h_load: cfs_rq->h_load:119, p->load_avg:26, cfs_rq->load_avg:14487
> <...>-26132 [000] 6571.361156: bprint: load_balance: detach_task migrate_load: task_h_load orginal: 0
>
> If cgroup has three levels(first tried), I can not find the task_h_load = 0 case.
Your system is is not large enough to face the problem
> group se's weight is relate to the task_group's share.
> task's weight is its weight.
>
> if (!tg->parent) {
> load = cpu_rq(cpu)->load.weight;
> } else {
> load = tg->parent->cfs_rq[cpu]->h_load;
> load *= tg->cfs_rq[cpu]->shares;
> load /= tg->parent->cfs_rq[cpu]->load.weight + 1;
> }
>
> I must reply to you even not find any clue. I falled in the trace flow.
>
> Thanks,
> Tao
>
> > > Some days ago, I tried this patch:
> > >
> > > https://lore.kernel.org/lkml/20200616164801.18644-1-peter.puhov@linaro.org/
> > >
> > > ---
> > > kernel/sched/fair.c | 8 +++++++-
> > > 1 file changed, 7 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index 02f323b85b6d..abcbdf80ee75 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -8662,8 +8662,14 @@ static bool update_pick_idlest(struct sched_group *idlest,
> > >
> > > case group_has_spare:
> > > /* Select group with most idle CPUs */
> > > - if (idlest_sgs->idle_cpus >= sgs->idle_cpus)
> > > + if (idlest_sgs->idle_cpus > sgs->idle_cpus)
> > > return false;
> > > +
> > > + /* Select group with lowest group_util */
> > > + if (idlest_sgs->idle_cpus == sgs->idle_cpus &&
> > > + idlest_sgs->group_util <= sgs->group_util)
> > > + return false;
> > > +
> > > break;
> > > }
> > >
> > > --
> > >
> > > This patch is related to wake up slow path and group type is full_busy.
> >
> > I tried it but haven't seen impacts on mmapfork test results
> >
> > > What I tried that got improved:
> > >
> > > $> sysbench threads --threads=16 run
> > >
> > > The total num of event(high is better):
> > >
> > > v5.8-rc1 : 34020 34494 33561
> > > v5.8-rc1+patch: 35466 36184 36260
> > >
> > > $> perf bench -f simple sched pipe -l 4000000
> > >
> > > v5.8-rc1 : 16.203 16.238 16.150
> > > v5.8-rc1+patch: 15.757 15.930 15.819
> > >
> > > I also saw some regressions about other workloads(dont know much).
> > > So, suggest to test this patch about this stress-ng.mmapfork. I didn't do
> > > this yet.
> > >
> > > Another patch i want to mention here is this(merged to V5.7 now):
> > >
> > > commit 68f7b5cc83 ("sched/cfs: change initial value of runnable_avg")
> > >
> > > And this regression happened based on V5.7. This patch is related to fork
> > > wake up path of overloaded type. Absolutely need to try then.
> > >
> > > Finally, I have given a patch that seems not related to fork wake up path,
> > > but I also tried it on some benchmark. But, did not saw improvement there.
> > > I also give this changed patch here(I realized that full_busy type idle cpu
> > > first but not sure). Maybe not need to try.
> > >
> > > Index: core.bak/kernel/sched/fair.c
> > > ===================================================================
> > > --- core.bak.orig/kernel/sched/fair.c
> > > +++ core.bak/kernel/sched/fair.c
> > > @@ -9226,17 +9226,20 @@ static struct sched_group *find_busiest_
> > > goto out_balanced;
> > >
> > > if (busiest->group_weight > 1 &&
> > > - local->idle_cpus <= (busiest->idle_cpus + 1))
> > > - /*
> > > - * If the busiest group is not overloaded
> > > - * and there is no imbalance between this and busiest
> > > - * group wrt idle CPUs, it is balanced. The imbalance
> > > - * becomes significant if the diff is greater than 1
> > > - * otherwise we might end up to just move the imbalance
> > > - * on another group. Of course this applies only if
> > > - * there is more than 1 CPU per group.
> > > - */
> > > - goto out_balanced;
> > > + local->idle_cpus <= (busiest->idle_cpus + 1)) {
> > > + if (local->group_type == group_has_spare) {
> > > + /*
> > > + * If the busiest group is not overloaded
> > > + * and there is no imbalance between this and busiest
> > > + * group wrt idle CPUs, it is balanced. The imbalance
> > > + * becomes significant if the diff is greater than 1
> > > + * otherwise we might end up to just move the imbalance
> > > + * on another group. Of course this applies only if
> > > + * there is more than 1 CPU per group.
> > > + */
> > > + goto out_balanced;
> > > + }
> > > + }
> > >
> > > if (busiest->sum_h_nr_running == 1)
> > > /*
> > >
> > >
> > > TBH, I don't know much about the below numbers.
> > >
> > > Thank you for the help!
> > >
> > > Thanks.
> > >
> > > > /*
> > > > * If the local group is less loaded than the selected
> > > >
> > > > --
> > > >
> > > >
> > > > > =========================================================================================
> > > > > tbox_group/testcase/rootfs/kconfig/compiler/nr_threads/disk/sc_pid_max/testtime/class/cpufreq_governor/ucode:
> > > > >
> > > > > lkp-bdw-ep6/stress-ng/debian-x86_64-20191114.cgz/x86_64-rhel-7.6/gcc-7/100%/1HDD/4194304/1s/scheduler/performance/0xb000038
> > > > >
> > > > > commit:
> > > > > e94f80f6c49020008e6fa0f3d4b806b8595d17d8
> > > > > 6c8116c914b65be5e4d6f66d69c8142eb0648c22
> > > > > v5.7
> > > > > c7e6d37f60da32f808140b1b7dabcc3cde73c4cc (Tao's patch)
> > > > >
> > > > > e94f80f6c4902000 6c8116c914b65be5e4d6f66d69c v5.7
> > > > > c7e6d37f60da32f808140b1b7da
> > > > > ---------------- --------------------------- ---------------------------
> > > > > ---------------------------
> > > > > %stddev %change %stddev %change %stddev %change
> > > > > %stddev
> > > > > \ | \ | \
> > > > > | \
> > > > > 819250 ± 5% -10.1% 736616 ± 8% +41.2% 1156877 ± 3%
> > > > > +43.6% 1176246 ± 5% stress-ng.futex.ops
> > > > > 818985 ± 5% -10.1% 736460 ± 8% +41.2% 1156215 ± 3%
> > > > > +43.6% 1176055 ± 5% stress-ng.futex.ops_per_sec
> > > > > 1551 ± 3% -3.4% 1498 ± 5% -4.6% 1480 ± 5%
> > > > > -14.3% 1329 ± 11% stress-ng.inotify.ops
> > > > > 1547 ± 3% -3.5% 1492 ± 5% -4.8% 1472 ± 5%
> > > > > -14.3% 1326 ± 11% stress-ng.inotify.ops_per_sec
> > > > > 11292 ± 8% -2.8% 10974 ± 8% -9.4% 10225 ± 6%
> > > > > -10.1% 10146 ± 6% stress-ng.kill.ops
> > > > > 11317 ± 8% -2.6% 11023 ± 8% -9.1% 10285 ± 5%
> > > > > -10.3% 10154 ± 6% stress-ng.kill.ops_per_sec
> > > > > 28.20 ± 4% -35.4% 18.22 -33.4% 18.77
> > > > > -27.7% 20.40 ± 9% stress-ng.mmapfork.ops_per_sec
> > > > > 2999012 ± 21% -10.1% 2696954 ± 22% -88.5% 344447 ± 11%
> > > > > -87.8% 364932 stress-ng.tee.ops_per_sec
> > > > > 7882 ± 3% -5.4% 7458 ± 4% -2.0% 7724 ± 3%
> > > > > -2.2% 7709 ± 4% stress-ng.vforkmany.ops
> > > > > 7804 ± 3% -5.2% 7400 ± 4% -2.0% 7647 ± 3%
> > > > > -2.1% 7636 ± 4% stress-ng.vforkmany.ops_per_sec
> > > > > 46745421 ± 3% -8.1% 42938569 ± 3% -5.2% 44312072 ± 4%
> > > > > -2.3% 45648193 stress-ng.yield.ops
> > > > > 46734472 ± 3% -8.1% 42926316 ± 3% -5.2% 44290338 ± 4%
> > > > > -2.4% 45627571 stress-ng.yield.ops_per_sec
> > > > >
> > > > >
> > > > >
> > > >
> > > > ...
> > > >
> > > > > --
> > > > > Zhengjun Xing
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