Messages in this thread | | | From | Paul Turner <> | Date | Mon, 27 Jun 2011 21:38:13 -0700 | Subject | Re: [patch 12/16] sched: prevent interactions with throttled entities |
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On Thu, Jun 23, 2011 at 4:49 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > On Tue, 2011-06-21 at 00:17 -0700, Paul Turner wrote: >> @@ -2635,8 +2704,10 @@ static int update_shares_cpu(struct task >> >> raw_spin_lock_irqsave(&rq->lock, flags); >> >> - update_rq_clock(rq); >> - update_cfs_load(cfs_rq, 1); >> + if (!throttled_hierarchy(cfs_rq)) { >> + update_rq_clock(rq); >> + update_cfs_load(cfs_rq, 1); >> + } >> >> /* > > OK, so we can't contribute to load since we're throttled, but > tg->load_weight might have changed meanwhile? >
What's why we continue to update their shares (also at enqueue/dequeue) but not their load, so that the weight will be correct when unthrottling*
> Also, update_cfs_shares()->reweight_entity() can dequeue/enqueue the > entity, doesn't that require an up-to-date rq->clock? >
It shouldn't, we're only doing an account_enqueue/dequeue, and there shouldn't be a cfs_rq->curr to lead to updates (on a throttled entity). I suppose we might do something interesting in the case of a race with alb forcing something throttled to run intersecting with update_shares()**.
The original concern here was [*] above, keeping shares current for the unthrottle. *However*, with the hierarchal throttle accounting in the current version, I think this can be improved.
Instead, we should skip update_shares/update_cfs_shares for all throttled entities and simply do a final update shares when throttle_count goes to 0 in tg_throttle_down (which also avoids **). I thought of doing this at the end of preparing the last patchset but by that time it was tested and I didn't want to change things around here at the last minute.
Will fix for this week.
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