Messages in this thread | | | Date | Mon, 10 Oct 2022 12:13:09 +0530 | From | Pavan Kondeti <> | Subject | Re: PSI idle-shutoff |
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On Mon, Oct 10, 2022 at 11:48:49AM +0530, Pavan Kondeti wrote: > On Sun, Oct 09, 2022 at 09:17:34PM +0800, Chengming Zhou wrote: > > On 2022/10/9 20:41, Chengming Zhou wrote: > > > Hello, > > > > > > I just saw these emails, sorry for late. > > > > > > On 2022/10/6 00:32, Suren Baghdasaryan wrote: > > >> On Sun, Oct 2, 2022 at 11:11 PM Suren Baghdasaryan <surenb@google.com> wrote: > > >>> > > >>> On Fri, Sep 16, 2022 at 10:45 PM Suren Baghdasaryan <surenb@google.com> wrote: > > >>>> > > >>>> On Wed, Sep 14, 2022 at 11:20 PM Pavan Kondeti > > >>>> <quic_pkondeti@quicinc.com> wrote: > > >>>>> > > >>>>> On Tue, Sep 13, 2022 at 07:38:17PM +0530, Pavan Kondeti wrote: > > >>>>>> 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. > > >>>> > > >>>> Hi Pavan, > > >>>> Thanks for reporting the issue. IIRC [1] was meant to fix exactly this > > >>>> issue. At the time it was written I tested it and it seemed to work. > > >>>> Maybe I missed something or some other change introduced afterwards > > >>>> affected the shutoff logic. I'll take a closer look next week when I'm > > >>>> back at my computer and will consult with Johannes. > > >>> > > >>> Sorry for the delay. I had some time to look into this and test psi > > >>> shutoff on my device and I think you are right. The patch I mentioned > > >>> prevents new psi_avgs_work from being scheduled when the only non-idle > > >>> task is psi_avgs_work itself, however the regular 2sec averaging work > > >>> will still go on. I think we could record the fact that the only > > >>> active task is psi_avgs_work in record_times() using a new > > >>> psi_group_cpu.state_mask flag and then prevent psi_avgs_work() from > > >>> rescheduling itself if that flag is set for all non-idle cpus. I'll > > >>> test this approach and will post a patch for review if that works. > > >> > > >> Hi Pavan, > > >> Testing PSI shutoff on Android proved more difficult than I expected. > > >> Lots of tasks to silence and I keep encountering new ones. > > >> The approach I was thinking about is something like this: > > >> > > >> --- > > >> include/linux/psi_types.h | 3 +++ > > >> kernel/sched/psi.c | 12 +++++++++--- > > >> 2 files changed, 12 insertions(+), 3 deletions(-) > > >> > > >> diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h > > >> index c7fe7c089718..8d936f22cb5b 100644 > > >> --- a/include/linux/psi_types.h > > >> +++ b/include/linux/psi_types.h > > >> @@ -68,6 +68,9 @@ enum psi_states { > > >> NR_PSI_STATES = 7, > > >> }; > > >> > > >> +/* state_mask flag to keep re-arming averaging work */ > > >> +#define PSI_STATE_WAKE_CLOCK (1 << NR_PSI_STATES) > > >> + > > >> enum psi_aggregators { > > >> PSI_AVGS = 0, > > >> PSI_POLL, > > >> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > > >> index ecb4b4ff4ce0..dd62ad28bacd 100644 > > >> --- a/kernel/sched/psi.c > > >> +++ b/kernel/sched/psi.c > > >> @@ -278,6 +278,7 @@ static void get_recent_times(struct psi_group > > >> *group, int cpu, > > >> if (delta) > > >> *pchanged_states |= (1 << s); > > >> } > > >> + *pchanged_states |= (state_mask & PSI_STATE_WAKE_CLOCK); > > > > > > If the avgs_work kworker is running on this CPU, it will still see > > > PSI_STATE_WAKE_CLOCK set in state_mask? So the work will be re-armed? > > > > > > Maybe I missed something... but I have another different idea which > > > I want to implement later only for discussion. > > > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > > index ee2ecc081422..f322e8fd8d41 100644 > > --- a/kernel/sched/psi.c > > +++ b/kernel/sched/psi.c > > @@ -241,11 +241,13 @@ static void get_recent_times(struct psi_group *group, int cpu, > > enum psi_aggregators aggregator, u32 *times, > > u32 *pchanged_states) > > { > > + int current_cpu = raw_smp_processor_id(); > > struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu); > > u64 now, state_start; > > enum psi_states s; > > unsigned int seq; > > u32 state_mask; > > + bool only_avgs_work = false; > > > > *pchanged_states = 0; > > > > @@ -256,6 +258,14 @@ static void get_recent_times(struct psi_group *group, int cpu, > > memcpy(times, groupc->times, sizeof(groupc->times)); > > state_mask = groupc->state_mask; > > state_start = groupc->state_start; > > + /* > > + * This CPU has only avgs_work kworker running, snapshot the > > + * newest times then don't need to re-arm work for this groupc. > > + * Normally this kworker will sleep soon and won't > > + * wake_clock in psi_group_change(). > > + */ > > + if (current_cpu == cpu && groupc->tasks[NR_RUNNING] == 1) > > + only_avgs_work = true; > > } while (read_seqcount_retry(&groupc->seq, seq)); > > > > /* Calculate state time deltas against the previous snapshot */ > > @@ -280,6 +290,10 @@ static void get_recent_times(struct psi_group *group, int cpu, > > if (delta) > > *pchanged_states |= (1 << s); > > } > > + > > + /* Clear PSI_NONIDLE so avgs_work won't be re-armed for this groupc */ > > + if (only_avgs_work) > > + *pchanged_states &= ~(1 << PSI_NONIDLE); > > } > > > Thanks Chengming for the patch. I will test this patch and report my > observations. It makes sense to consider this CPU as non-idle if the PSI kworker > is the only task running. It could run other works but that decision is now > deferred to schedule out path. Ideally if this is the only (or last) work > running, we should not see PSI work not re-arming it self. >
is condition groupc->tasks[NR_RUNNING] == 1 alone sufficient to clear NONIDLE? or should we also make sure that !NR_IOWAIT && !NR_MEMSTALL condition on this CPU?
Thanks, Pavan
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