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Date: Fri, 14 Oct 2022 10:18:32 -0400 From: Johannes Weiner <hannes@...xchg.org> To: Chengming Zhou <zhouchengming@...edance.com> Cc: surenb@...gle.com, quic_pkondeti@...cinc.com, peterz@...radead.org, quic_charante@...cinc.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2] sched/psi: Fix avgs_work re-arm in psi_avgs_work() On Fri, Oct 14, 2022 at 07:05:51PM +0800, Chengming Zhou wrote: > Pavan reported a problem that PSI avgs_work idle shutoff is not > working at all. Because PSI_NONIDLE condition would be observed in > psi_avgs_work()->collect_percpu_times()->get_recent_times() even if > only the kworker running avgs_work on the CPU. > > Although commit 1b69ac6b40eb ("psi: fix aggregation idle shut-off") > avoided the ping-pong wake problem when the worker sleep, psi_avgs_work() > still will always re-arm the avgs_work, so shutoff is not working. > > This patch changes to use PSI_STATE_RESCHEDULE to flag whether to > re-arm avgs_work in get_recent_times(). For the current CPU, we re-arm > avgs_work only when (NR_RUNNING > 1 || NR_IOWAIT > 0 || NR_MEMSTALL > 0), > for other CPUs we can just check PSI_NONIDLE delta. The new flag > is only used in psi_avgs_work(), so we check in get_recent_times() > that current_work() is avgs_work. > > One potential problem is that the brief period of non-idle time > incurred between the aggregation run and the kworker's dequeue will > be stranded in the per-cpu buckets until avgs_work run next time. > The buckets can hold 4s worth of time, and future activity will wake > the avgs_work with a 2s delay, giving us 2s worth of data we can leave > behind when shut off the avgs_work. If the kworker run other works after > avgs_work shut off and doesn't have any scheduler activities for 2s, > this maybe a problem. > > Reported-by: Pavan Kondeti <quic_pkondeti@...cinc.com> > Signed-off-by: Chengming Zhou <zhouchengming@...edance.com> Acked-by: Johannes Weiner <hannes@...xchg.org>
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