Messages in this thread Patch in this message | | | Date | Thu, 2 Mar 2023 17:36:13 +0800 | Subject | Re: [PATCH v3] sched/fair: sanitize vruntime of entity being placed | From | Zhang Qiao <> |
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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) + 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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