Messages in this thread Patch in this message | | | Date | Mon, 16 Nov 2020 16:42:32 +0000 | From | Mel Gorman <> | Subject | Re: Loadavg accounting error on arm64 |
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On Mon, Nov 16, 2020 at 03:29:46PM +0000, Mel Gorman wrote: > I did, it was the on_cpu ordering for the blocking case that had me > looking at the smp_store_release and smp_cond_load_acquire in arm64 in > the first place thinking that something in there must be breaking the > on_cpu ordering. I'm re-reading it every so often while trying to figure > out where the gap is or whether I'm imagining things. > > Not fully tested but did not instantly break either > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index d2003a7d5ab5..877eaeba45ac 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4459,14 +4459,26 @@ static void __sched notrace __schedule(bool preempt) > if (signal_pending_state(prev_state, prev)) { > prev->state = TASK_RUNNING; > } else { > - prev->sched_contributes_to_load = > + int acct_load = > (prev_state & TASK_UNINTERRUPTIBLE) && > !(prev_state & TASK_NOLOAD) && > !(prev->flags & PF_FROZEN); > > - if (prev->sched_contributes_to_load) > + prev->sched_contributes_to_load = acct_load; > + if (acct_load) { > rq->nr_uninterruptible++; > > + /* > + * Pairs with p->on_cpu ordering, either a > + * smp_load_acquire or smp_cond_load_acquire > + * in the ttwu path before ttwu_do_activate > + * p->sched_contributes_to_load. It's only > + * after the nr_interruptible update happens > + * that the ordering is critical. > + */ > + smp_wmb(); > + } > + > /* > * __schedule() ttwu() > * prev_state = prev->state; if (p->on_rq && ...) >
This passed the test. Load averages taken once a minute after the test completed showed
950.21 977.17 990.69 1/853 2117 349.00 799.32 928.69 1/859 2439 128.18 653.85 870.56 1/861 2736 47.08 534.84 816.08 1/860 3029 17.29 437.50 765.00 1/865 3357 6.35 357.87 717.13 1/865 3653 2.33 292.74 672.24 1/861 3709 0.85 239.46 630.17 1/859 3711 0.31 195.87 590.73 1/857 3713 0.11 160.22 553.76 1/853 3715
With 5.10-rc3, it got stuck with a load average of 244 after the test completed even though the machine was idle.
-- Mel Gorman SUSE Labs
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