Vincent Guittot writes: > Hi Dietmar and Ying, > > Le Tuesday 03 Jan 2017 11:38:39 (+0100), Dietmar Eggemann a crit : >> Hi Vincent and Ying, >> >> On 01/02/2017 04:42 PM, Vincent Guittot wrote: >> >Hi Ying, >> > >> >On 28 December 2016 at 09:17, Huang, Ying wrote: >> >>Vincent Guittot writes: >> >> >> >>>Le Tuesday 13 Dec 2016 . 09:47:30 (+0800), Huang, Ying a .crit : >> >>>>Hi, Vincent, >> >>>> >> >>>>Vincent Guittot writes: >> >> [...] >> > > [snip] > >> >> >> >>The test result is as follow, >> >> >> >>========================================================================================= >> >>compiler/cpufreq_governor/freq/kconfig/nr_task/rootfs/samples/tbox_group/test/testcase: >> >> gcc-6/powersave/20/x86_64-rhel-7.2/100%/debian-x86_64-2016-08-31.cgz/6000ss/lkp-hsw-d01/cache/ftq >> >> >> >>commit: >> >> 4e5160766fcc9f41bbd38bac11f92dce993644aa: first bad commit >> >> 09a43ace1f986b003c118fdf6ddf1fd685692d49: parent of first bad commit >> >> 0613870ea53a7a279d8d37f2a3ce40aafc155fc8: debug commit with above patch >> >> >> >>4e5160766fcc9f41 09a43ace1f986b003c118fdf6d 0613870ea53a7a279d8d37f2a3 >> >>---------------- -------------------------- -------------------------- >> >> %stddev %change %stddev %change %stddev >> >> \ | \ | \ >> >> 61670 228% -96.5% 2148 11% -94.7% 3281 58% ftq.noise.25% >> >> 3463 10% -60.0% 1386 19% -26.3% 2552 58% ftq.noise.50% >> >> 1116 23% -72.6% 305.99 30% -35.8% 716.15 64% ftq.noise.75% >> >> 3843815 3% +3.1% 3963589 1% -49.6% 1938221 100% ftq.time.involuntary_context_switches >> >> 5.33 30% +21.4% 6.46 14% -71.7% 1.50 108% time.system_time >> >> >> >> >> >>It appears that the system_time and involuntary_context_switches reduced >> >>much after applied the debug patch, which is good from noise point of >> >>view. ftq.noise.50% reduced compared with the first bad commit, but >> >>have not restored to that of the parent of the first bad commit. >> > >> >Thanks for testing. I will try to improve it a bit but not sure that I >> >can reduce more. >> >> Is this a desktop system where this regression comes from autogroups (1 >> level taskgroups) or a server system with systemd (2 level taskgroups)? >> >> Since the PELT rewrite (v4.2) I have ~60 autogroups per cpu >> (&rq->leaf_cfs_rq_list) on my Ubuntu desktop system permanently (Intel >> i7-4750HQ) whereas in v4.1 there were 0 - 10. >> >> $ for i in `seq 0 7`; do cat /proc/sched_debug | grep >> "cfs_rq\[$i\]:/autogroup-" | wc -l; done >> 58 >> 61 >> 63 >> 65 >> 60 >> 59 >> 62 >> 56 >> >> Couldn't we still remove these autogroups by if (!cfs_rq->nr_running && >> !se->avg.load_avg && !se->avg.util_avg) in update_blocked_averages()? >> >> Vincent, like we discussed in September last year, the proper fix would >> probably be a cfs-rq->nr_attached which IMHO is not doable w/o being an >> atomic because of migrate_task_rq_fair()->remove_entity_load_avg() not >> holding the rq lock. > > I remember the discussion and even if I agree that a large number of taskgroup > increases the number of loop in update_blocked_averages() and as a result the > time spent in the update, I don't think that this is the root cause of > this regression because the patch "sched/fair: Propagate asynchrous detach" > doesn't add more loops to update_blocked_averages but it adds more thing to do > per loop. > > Then, I think I'm still too conservative in the condition for calling > update_load_avg(cfs_rq->tg->se[cpu], 0). This call has been added to > propagate gcfs_rq->propagate_avg flag to parent so we don't need to call it > even if load_avg is not null but only when propagate_avg flag is set. The > patch below should improve thing compare to the previous version because > it will call update_load_avg(cfs_rq->tg->se[cpu], 0) only if an asynchrounous > detach happened (propagate_avg is set). > > Ying, could you test the patch below instead of the previous one ? > > --- > kernel/sched/fair.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 6559d19..a4f5c35 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6915,6 +6915,7 @@ static void update_blocked_averages(int cpu) > { > struct rq *rq = cpu_rq(cpu); > struct cfs_rq *cfs_rq; > + struct sched_entity *se; > unsigned long flags; > > raw_spin_lock_irqsave(&rq->lock, flags); > @@ -6932,9 +6933,10 @@ static void update_blocked_averages(int cpu) > if (update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq, true)) > update_tg_load_avg(cfs_rq, 0); > > - /* Propagate pending load changes to the parent */ > - if (cfs_rq->tg->se[cpu]) > - update_load_avg(cfs_rq->tg->se[cpu], 0); > + /* Propagate pending load changes to the parent if any */ > + se = cfs_rq->tg->se[cpu]; > + if (se && cfs_rq->propagate_avg) > + update_load_avg(se, 0); > } > raw_spin_unlock_irqrestore(&rq->lock, flags); > } Here is the test result, ========================================================================================= compiler/cpufreq_governor/freq/kconfig/nr_task/rootfs/samples/tbox_group/test/testcase: gcc-6/powersave/20/x86_64-rhel-7.2/100%/debian-x86_64-2016-08-31.cgz/6000ss/lkp-hsw-d01/cache/ftq commit: 4e5160766fcc9f41bbd38bac11f92dce993644aa: first bad commit 09a43ace1f986b003c118fdf6ddf1fd685692d49: parent of first bad commit b524060933c546fd2410c5a09360ba23a0fef846: with fix patch above 4e5160766fcc9f41 09a43ace1f986b003c118fdf6d b524060933c546fd2410c5a093 ---------------- -------------------------- -------------------------- %stddev %change %stddev %change %stddev \ | \ | \ 3463 ± 10% -61.4% 1335 ± 17% -3.0% 3359 ± 2% ftq.noise.50% 1116 ± 23% -73.7% 293.90 ± 30% -23.8% 850.69 ± 17% ftq.noise.75% Best Regards, Huang, Ying