Messages in this thread | | | Subject | Re: [PATCH] sched/fair: don't assign runtime for throttled cfs_rq | From | Liangyan <> | Date | Tue, 27 Aug 2019 10:45:00 +0800 |
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On 19/8/27 上午1:38, bsegall@google.com wrote: > Valentin Schneider <valentin.schneider@arm.com> writes: > >> On 23/08/2019 21:00, bsegall@google.com wrote: >> [...] >>> Could you mention in the message that this a throttled cfs_rq can have >>> account_cfs_rq_runtime called on it because it is throttled before >>> idle_balance, and the idle_balance calls update_rq_clock to add time >>> that is accounted to the task. >>> >> >> Mayhaps even a comment for the extra condition. >> >>> I think this solution is less risky than unthrottling >>> in this area, so other than that: >>> >>> Reviewed-by: Ben Segall <bsegall@google.com> >>> >> >> If you don't mind squashing this in: >> >> -----8<----- >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index b1d9cec9b1ed..b47b0bcf56bc 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -4630,6 +4630,10 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b, u64 remaining) >> if (!cfs_rq_throttled(cfs_rq)) >> goto next; >> >> + /* By the above check, this should never be true */ >> + WARN_ON(cfs_rq->runtime_remaining > 0); >> + >> + /* Pick the minimum amount to return to a positive quota state */ >> runtime = -cfs_rq->runtime_remaining + 1; >> if (runtime > remaining) >> runtime = remaining; >> ----->8----- >> >> I'm not adamant about the extra comment, but the WARN_ON would be nice IMO. >> >> >> @Ben, do you reckon we want to strap >> >> Cc: <stable@vger.kernel.org> >> Fixes: ec12cb7f31e2 ("sched: Accumulate per-cfs_rq cpu usage and charge against bandwidth") >> >> to the thing? AFAICT the pick_next_task_fair() + idle_balance() dance you >> described should still be possible on that commit. > > I'm not sure about stable policy in general, but it seems reasonable. > The WARN_ON might want to be WARN_ON_ONCE, and it seems fine to have it > or not.
Thanks Ben and Valentin for all of the comments. Per Xunlei's suggestion, I used SCHED_WARN_ON instead in v3. Regarding whether cc stable, I'm also not sure.
> >> >> >> Other than that, >> >> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> >> >> [...]
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