Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 2 Mar 2023 14:34:19 +0100 | Subject | Re: [PATCH v3] sched/fair: sanitize vruntime of entity being placed |
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On Thu, 2 Mar 2023 at 10:36, Zhang Qiao <zhangqiao22@huawei.com> wrote: > > > > 在 2023/2/27 22:37, Vincent Guittot 写道: > > On Mon, 27 Feb 2023 at 09:43, Roman Kagan <rkagan@amazon.de> wrote: > >> > >> On Tue, Feb 21, 2023 at 06:26:11PM +0100, Vincent Guittot wrote: > >>> On Tue, 21 Feb 2023 at 17:57, Roman Kagan <rkagan@amazon.de> wrote: > >>>> What scares me, though, is that I've got a message from the test robot > >>>> that this commit drammatically affected hackbench results, see the quote > >>>> below. I expected the commit not to affect any benchmarks. > >>>> > >>>> Any idea what could have caused this change? > >>> > >>> Hmm, It's most probably because se->exec_start is reset after a > >>> migration and the condition becomes true for newly migrated task > >>> whereas its vruntime should be after min_vruntime. > >>> > >>> We have missed this condition > >> > >> Makes sense to me. > >> > >> But what would then be the reliable way to detect a sched_entity which > >> has slept for long and risks overflowing in .vruntime comparison? > > > > For now I don't have a better idea than adding the same check in > > migrate_task_rq_fair() > > Hi, Vincent, > I fixed this condition as you said, and the test results are as follows. > > testcase: hackbench -g 44 -f 20 --process --pipe -l 60000 -s 100 > version1: v6.2 > version2: v6.2 + commit 829c1651e9c4 > version3: v6.2 + commit 829c1651e9c4 + this patch > > ------------------------------------------------- > version1 version2 version3 > test1 81.0 118.1 82.1 > test2 82.1 116.9 80.3 > test3 83.2 103.9 83.3 > avg(s) 82.1 113.0 81.9 > > ------------------------------------------------- > After deal with the task migration case, the hackbench result has restored. > > The patch as follow, how does this look? > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index ff4dbbae3b10..3a88d20fd29e 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4648,6 +4648,26 @@ static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se) > #endif > } > > +static inline u64 sched_sleeper_credit(struct sched_entity *se) > +{ > + > + unsigned long thresh; > + > + if (se_is_idle(se)) > + thresh = sysctl_sched_min_granularity; > + else > + thresh = sysctl_sched_latency; > + > + /* > + * Halve their sleep time's effect, to allow > + * for a gentler effect of sleepers: > + */ > + if (sched_feat(GENTLE_FAIR_SLEEPERS)) > + thresh >>= 1; > + > + return thresh; > +} > + > static void > place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > { > @@ -4664,23 +4684,8 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > vruntime += sched_vslice(cfs_rq, se); > > /* sleeps up to a single latency don't count. */ > - if (!initial) { > - unsigned long thresh; > - > - if (se_is_idle(se)) > - thresh = sysctl_sched_min_granularity; > - else > - thresh = sysctl_sched_latency; > - > - /* > - * Halve their sleep time's effect, to allow > - * for a gentler effect of sleepers: > - */ > - if (sched_feat(GENTLE_FAIR_SLEEPERS)) > - thresh >>= 1; > - > - vruntime -= thresh; > - } > + if (!initial) > + vruntime -= sched_sleeper_credit(se); > > /* > * Pull vruntime of the entity being placed to the base level of > @@ -4690,7 +4695,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > * inversed due to s64 overflow. > */ > sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; > - if ((s64)sleep_time > 60LL * NSEC_PER_SEC) > + if (se->exec_start != 0 && (s64)sleep_time > 60LL * NSEC_PER_SEC) > se->vruntime = vruntime; > else > se->vruntime = max_vruntime(se->vruntime, vruntime); > @@ -7634,8 +7639,12 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) > */ > if (READ_ONCE(p->__state) == TASK_WAKING) { > struct cfs_rq *cfs_rq = cfs_rq_of(se); > + u64 sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; > > - se->vruntime -= u64_u32_load(cfs_rq->min_vruntime); > + if ((s64)sleep_time > 60LL * NSEC_PER_SEC)
You also need to test (se->exec_start !=0) here because the task might migrate another time before being scheduled. You should create a helper function like below and use it in both place
static inline bool entity_long_sleep(se) { struct cfs_rq *cfs_rq; u64 sleep_time;
if (se->exec_start == 0) return false;
cfs_rq = cfs_rq_of(se); sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; if ((s64)sleep_time > 60LL * NSEC_PER_SEC) return true;
return false; }
> + se->vruntime = -sched_sleeper_credit(se); > + else > + se->vruntime -= u64_u32_load(cfs_rq->min_vruntime); > } > > if (!task_on_rq_migrating(p)) { > > > > Thanks. > Zhang Qiao. > > > > >> > >> Thanks, > >> Roman. > >> > >> > >> > >> Amazon Development Center Germany GmbH > >> Krausenstr. 38 > >> 10117 Berlin > >> Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss > >> Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B > >> Sitz: Berlin > >> Ust-ID: DE 289 237 879 > >> > >> > >> > > . > >
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