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dkim=pass header.d=google.com header.s=20210112 header.b=SbI+5adg; spf=pass (imf19.hostedemail.com: domain of surenb@google.com designates 209.85.128.181 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: jqw99814yd8jmz7fzqwu5okgxcbyr557 X-Rspamd-Queue-Id: DF13A1A0021 X-HE-Tag: 1665436598-312365 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Oct 10, 2022 at 3:57 AM Hillf Danton wrote: > > On 13 Sep 2022 19:38:17 +0530 Pavan Kondeti > > Hi > > > > The fact that psi_avgs_work()->collect_percpu_times()->get_recent_times() > > run from a kworker thread, PSI_NONIDLE condition would be observed as > > there is a RUNNING task. So we would always end up re-arming the work. > > > > If the work is re-armed from the psi_avgs_work() it self, the backing off > > logic in psi_task_change() (will be moved to psi_task_switch soon) can't > > help. The work is already scheduled. so we don't do anything there. > > > > Probably I am missing some thing here. Can you please clarify how we > > shut off re-arming the psi avg work? > > Instead of open coding schedule_delayed_work() in bid to check if timer > hits the idle task (see delayed_work_timer_fn()), the idle task is tracked > in psi_task_switch() and checked by kworker to see if it preempted the idle > task. > > Only for thoughts now. > > Hillf > > +++ b/kernel/sched/psi.c > @@ -412,6 +412,8 @@ static u64 update_averages(struct psi_gr > return avg_next_update; > } > > +static DEFINE_PER_CPU(int, prev_task_is_idle); > + > static void psi_avgs_work(struct work_struct *work) > { > struct delayed_work *dwork; > @@ -439,7 +441,7 @@ static void psi_avgs_work(struct work_st > if (now >= group->avg_next_update) > group->avg_next_update = update_averages(group, now); > > - if (nonidle) { > + if (nonidle && 0 == per_cpu(prev_task_is_idle, raw_smp_processor_id())) { This condition would be incorrect if nonidle was set by a cpu other than raw_smp_processor_id() and prev_task_is_idle[raw_smp_processor_id()] == 0. IOW, if some activity happens on a non-current cpu, we would fail to reschedule psi_avgs_work for it. This can be fixed in collect_percpu_times() by considering prev_task_is_idle for all other CPUs as well. However Chengming's approach seems simpler to me TBH and does not require an additional per-cpu variable. > schedule_delayed_work(dwork, nsecs_to_jiffies( > group->avg_next_update - now) + 1); > } > @@ -859,6 +861,7 @@ void psi_task_switch(struct task_struct > if (prev->pid) { > int clear = TSK_ONCPU, set = 0; > > + per_cpu(prev_task_is_idle, cpu) = 0; > /* > * When we're going to sleep, psi_dequeue() lets us > * handle TSK_RUNNING, TSK_MEMSTALL_RUNNING and > @@ -888,7 +891,8 @@ void psi_task_switch(struct task_struct > for (; group; group = iterate_groups(prev, &iter)) > psi_group_change(group, cpu, clear, set, now, true); > } > - } > + } else > + per_cpu(prev_task_is_idle, cpu) = 1; > } > > /** >