Messages in this thread | | | Subject | Re: [PATCH -v2 07/17] sched: Fix hotplug vs CPU bandwidth control | From | Dietmar Eggemann <> | Date | Mon, 12 Oct 2020 16:14:31 +0200 |
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On 12/10/2020 15:18, Peter Zijlstra wrote: > On Mon, Oct 12, 2020 at 02:52:00PM +0200, Peter Zijlstra wrote: >> On Fri, Oct 09, 2020 at 10:41:11PM +0200, Dietmar Eggemann wrote: >>> On 05/10/2020 16:57, Peter Zijlstra wrote: >>>> Since we now migrate tasks away before DYING, we should also move >>>> bandwidth unthrottle, otherwise we can gain tasks from unthrottle >>>> after we expect all tasks to be gone already. >>>> >>>> Also; it looks like the RT balancers don't respect cpu_active() and >>>> instead rely on rq->online in part, complete this. This too requires >>>> we do set_rq_offline() earlier to match the cpu_active() semantics. >>>> (The bigger patch is to convert RT to cpu_active() entirely) >>>> >>>> Since set_rq_online() is called from sched_cpu_activate(), place >>>> set_rq_offline() in sched_cpu_deactivate(). >> >>> [ 76.215229] WARNING: CPU: 1 PID: 1913 at kernel/irq_work.c:95 irq_work_queue_on+0x108/0x110 >> >>> [ 76.341076] irq_work_queue_on+0x108/0x110 >>> [ 76.349185] pull_rt_task+0x58/0x68 >>> [ 76.352673] balance_rt+0x84/0x88 >> >>> balance_rt() checks via need_pull_rt_task() that rq is online but it >>> looks like that with RT_PUSH_IPI pull_rt_task() -> tell_cpu_to_push() >>> calls irq_work_queue_on() with cpu = rto_next_cpu(rq->rd) and this one >>> can be offline here as well now. >> >> Hurmph... so if I read this right, we reach offline with overload set? >> >> Oooh, I think I see how that happens.. > > I think the below two hunks need to be reverted from the patch. Can you > confirm? > > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -2326,9 +2326,6 @@ static void rq_online_dl(struct rq *rq) > /* Assumes rq->lock is held */ > static void rq_offline_dl(struct rq *rq) > { > - if (rq->dl.overloaded) > - dl_clear_overload(rq); > - > cpudl_clear(&rq->rd->cpudl, rq->cpu); > cpudl_clear_freecpu(&rq->rd->cpudl, rq->cpu); > } > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -2245,9 +2245,6 @@ static void rq_online_rt(struct rq *rq) > /* Assumes rq->lock is held */ > static void rq_offline_rt(struct rq *rq) > { > - if (rq->rt.overloaded) > - rt_clear_overload(rq); > - > __disable_runtime(rq); > > cpupri_set(&rq->rd->cpupri, rq->cpu, CPUPRI_INVALID); >
Yes, this seems to fix it. Tested with RT testcase for > 20min. This issue did appear within 30 secs w/o this fix.
Looks like that we now bail out of pull_rt_task() in one of the rt_overload_count related conditions before we call RT_PUSH_IPI functionality (tell_cpu_to_push()).
Debug snippet w/o this fix with extra output in tell_cpu_to_push():
[ 128.608880] sched: RT throttling activated [ 204.240351] CPU2 cpu=0 is offline rt_overloaded=1 [ 204.245069] ------------[ cut here ]------------ [ 204.249697] WARNING: CPU: 2 PID: 19 at kernel/irq_work.c:95 irq_work_queue_on+0x108/0x110
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