Messages in this thread | | | From | Paul Turner <> | Date | Thu, 14 Oct 2010 02:14:56 -0700 | Subject | Re: [PATCH v3 2/7] sched: accumulate per-cfs_rq cpu usage |
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On Thu, Oct 14, 2010 at 2:01 AM, Peter Zijlstra <peterz@infradead.org> wrote: > On Tue, 2010-10-12 at 13:21 +0530, Bharata B Rao wrote: >> +static void account_cfs_rq_quota(struct cfs_rq *cfs_rq, >> + unsigned long delta_exec) >> +{ >> + if (cfs_rq->quota_assigned == RUNTIME_INF) >> + return; >> + >> + cfs_rq->quota_used += delta_exec; >> + >> + if (cfs_rq->quota_used < cfs_rq->quota_assigned) >> + return; >> + >> + cfs_rq->quota_assigned += tg_request_cfs_quota(cfs_rq->tg); >> +} > > That looks iffy, quota_assigned is only ever incremented and can wrap.
This can't advance at a rate faster than ~vruntime and we can't handle wrapping there anyway (fortunately it would take something like 35k years?)
> Why not subtract delta_exec and replenish when <0? That keeps the > numbers small. >
Accounting in the opposite direction allows us to catch-up in subsequent periods when a task exceeds its bandwidth across an interval where we are not able to immediately throttle it (e.g. costly syscall without config_prempt). Since we'll continue to accrue the execution time in this case it will be effectively pre-charged against the next slice received. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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