Messages in this thread | | | Date | Sun, 9 Oct 2022 20:41:41 +0800 | Subject | Re: PSI idle-shutoff | From | Chengming Zhou <> |
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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.
Thanks.
> } > > static void calc_avgs(unsigned long avg[3], int missed_periods, > @@ -413,7 +414,7 @@ static void psi_avgs_work(struct work_struct *work) > struct delayed_work *dwork; > struct psi_group *group; > u32 changed_states; > - bool nonidle; > + bool wake_clock; > u64 now; > > dwork = to_delayed_work(work); > @@ -424,7 +425,7 @@ static void psi_avgs_work(struct work_struct *work) > now = sched_clock(); > > collect_percpu_times(group, PSI_AVGS, &changed_states); > - nonidle = changed_states & (1 << PSI_NONIDLE); > + wake_clock = changed_states & PSI_STATE_WAKE_CLOCK; > /* > * If there is task activity, periodically fold the per-cpu > * times and feed samples into the running averages. If things > @@ -435,7 +436,7 @@ static void psi_avgs_work(struct work_struct *work) > if (now >= group->avg_next_update) > group->avg_next_update = update_averages(group, now); > > - if (nonidle) { > + if (wake_clock) { > schedule_delayed_work(dwork, nsecs_to_jiffies( > group->avg_next_update - now) + 1); > } > @@ -742,6 +743,11 @@ static void psi_group_change(struct psi_group > *group, int cpu, > if (unlikely(groupc->tasks[NR_ONCPU] && cpu_curr(cpu)->in_memstall)) > state_mask |= (1 << PSI_MEM_FULL); > > + if (wake_clock || test_state(groupc->tasks, PSI_NONIDLE)) { > + /* psi_avgs_work was not the only task on the CPU */ > + state_mask |= PSI_STATE_WAKE_CLOCK; > + } > + > groupc->state_mask = state_mask; > > write_seqcount_end(&groupc->seq);
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