Messages in this thread | | | Date | Thu, 2 Aug 2018 14:18:51 +0100 | From | Quentin Perret <> | Subject | Re: [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator |
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On Thursday 02 Aug 2018 at 15:08:01 (+0200), Peter Zijlstra wrote: > On Thu, Aug 02, 2018 at 02:03:38PM +0100, Quentin Perret wrote: > > On Thursday 02 Aug 2018 at 14:26:29 (+0200), Peter Zijlstra wrote: > > > On Tue, Jul 24, 2018 at 01:25:16PM +0100, Quentin Perret wrote: > > > > @@ -5100,8 +5118,17 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) > > > > update_cfs_group(se); > > > > } > > > > > > > > - if (!se) > > > > + if (!se) { > > > > add_nr_running(rq, 1); > > > > + /* > > > > + * The utilization of a new task is 'wrong' so wait for it > > > > + * to build some utilization history before trying to detect > > > > + * the overutilized flag. > > > > + */ > > > > + if (flags & ENQUEUE_WAKEUP) > > > > + update_overutilized_status(rq); > > > > + > > > > + } > > > > > > > > hrtick_update(rq); > > > > } > > > > > > That is a somewhat dodgy hack. There is no guarantee what so ever that > > > when the task wakes next its history is any better. The comment doesn't > > > reflect this I feel. > > > > AFAICT the main use-case here is to avoid re-enabling the load balance > > and ruining all the task placement because of a tiny task. I don't > > really see how we can do that differently ... > > Sure I realize that.. but it doesn't completely avoid it. Suppose this > new task instantly blocks and wakes up again. Then its util signal will > be exactly what you didn't want but we'll account it and cause the above > scenario you wanted to avoid.
That is true. ... I also realize now that this patch was written long before util_est, and that also has an impact here, especially in the scenario you described where the task blocks. So any wake-up after the first enqueue will risk to overutilize the system, even if the task blocked for ages.
Hmm ...
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