* Mike Galbraith <efault@xxxxxx> wrote: > On Tue, 2023-08-22 at 08:33 +0530, K Prateek Nayak wrote: > > Hello Mike, > > Greetings! > > > > FWIW, there are more tbench shards lying behind EEVDF than in front. > > > > > > tbench 8 on old i7-4790 box > > > 4.4.302 4024 > > > 6.4.11 3668 > > > 6.4.11-eevdf 3522 > > > > > > > I agree, but on servers, tbench has been useful to identify a variety of > > issues [1][2][3] and I believe it is better to pick some shards up than > > leave them lying around for others to step on :) > > Absolutely, but in this case it isn't due to various overheads wiggling > about and/or bitrot, everything's identical except the scheduler, and > its overhead essentially is too. > > taskset -c 3 pipe-test > 6.4.11 1.420033 usecs/loop -- avg 1.420033 1408.4 KHz > 6.4.11-eevdf 1.413024 usecs/loop -- avg 1.413024 1415.4 KHz > > Methinks these shards are due to tbench simply being one of those > things that happens to like the CFS notion of short term fairness a bit > better than the EEVDF notion, ie are inevitable fallout tied to the > very thing that makes EEVDF service less spiky that CFS, and thus will > be difficult to sweep up. > > Too bad I didn't save Peter's test hack to make EEVDF use the same > notion of fair (not a keeper) as I think that would likely prove it. BTW., if overscheduling is still an issue, I'm wondering whether we could go so far as to turn off wakeup preemption for same-prio SCHED_OTHER tasks altogether, as per the attached patch? What does this do to your various tests? Test booted only. Thanks, Ingo =============> From: Ingo Molnar <mingo@xxxxxxxxxx> Date: Tue, 19 Sep 2023 10:49:51 +0200 Subject: [PATCH] sched/fair: Do not wakeup-preempt same-prio SCHED_OTHER tasks Reduce overscheduling some more: do not wakeup-preempt same-priority SCHED_OTHER tasks. Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a502e3255392..98efe01c8e4e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8042,7 +8042,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int * Batch and idle tasks do not preempt non-idle tasks (their preemption * is driven by the tick): */ - if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION)) + if (unlikely(p->policy != SCHED_NORMAL) || likely(p->prio == curr->prio) || !sched_feat(WAKEUP_PREEMPTION)) return; find_matching_se(&se, &pse);
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