[tip:,sched/core] sched/psi: Fix avgs_work re-arm in psi_avgs_work()

  The following commit has been merged into the sched/core branch of tip:

Commit-ID:     7d89d7bb921c5ae5a428df282e64ee5692e26fe0
Gitweb:        https://git.kernel.org/tip/7d89d7bb921c5ae5a428df282e64ee5692e26fe0
Author:        Chengming Zhou <zhouchengming@bytedance.com>
AuthorDate:    Mon, 10 Oct 2022 18:42:06 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 27 Oct 2022 11:01:23 +02:00

sched/psi: Fix avgs_work re-arm in psi_avgs_work()

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 consider current CPU groupc as IDLE if the
kworker running avgs_work is the only task running and no IOWAIT
or MEMSTALL sleep tasks, in which case we will shut off the avgs_work
if other CPUs' groupc are also IDLE.

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@quicinc.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221010104206.12184-1-zhouchengming@bytedance.com
---
 kernel/sched/psi.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
  

Hello,

Thanks for picking this up. There is a newer version which has been acked:
https://lore.kernel.org/all/20221014110551.22695-1-zhouchengming@bytedance.com/

As well another PSI patch that has been acked by Johannes:
https://lore.kernel.org/all/20220926081931.45420-1-zhouchengming@bytedance.com/

Thanks!


On 2022/10/28 14:42, tip-bot2 for Chengming Zhou wrote:
> The following commit has been merged into the sched/core branch of tip:
> 
> Commit-ID:     7d89d7bb921c5ae5a428df282e64ee5692e26fe0
> Gitweb:        https://git.kernel.org/tip/7d89d7bb921c5ae5a428df282e64ee5692e26fe0
> Author:        Chengming Zhou <zhouchengming@bytedance.com>
> AuthorDate:    Mon, 10 Oct 2022 18:42:06 +08:00
> Committer:     Peter Zijlstra <peterz@infradead.org>
> CommitterDate: Thu, 27 Oct 2022 11:01:23 +02:00
> 
> sched/psi: Fix avgs_work re-arm in psi_avgs_work()
> 
> 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 consider current CPU groupc as IDLE if the
> kworker running avgs_work is the only task running and no IOWAIT
> or MEMSTALL sleep tasks, in which case we will shut off the avgs_work
> if other CPUs' groupc are also IDLE.
> 
> 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@quicinc.com>
> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Link: https://lore.kernel.org/r/20221010104206.12184-1-zhouchengming@bytedance.com
> ---
>  kernel/sched/psi.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index ee2ecc0..f4cdf6f 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -242,6 +242,8 @@ static void get_recent_times(struct psi_group *group, int cpu,
>  			     u32 *pchanged_states)
>  {
>  	struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
> +	int current_cpu = raw_smp_processor_id();
> +	bool only_avgs_work = false;
>  	u64 now, state_start;
>  	enum psi_states s;
>  	unsigned int seq;
> @@ -256,6 +258,15 @@ 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 for this groupc.
> +		 * Normally this kworker will sleep soon and won't wake
> +		 * avgs_work back up in psi_group_change().
> +		 */
> +		if (current_cpu == cpu && groupc->tasks[NR_RUNNING] == 1 &&
> +		    !groupc->tasks[NR_IOWAIT] && !groupc->tasks[NR_MEMSTALL])
> +			only_avgs_work = true;
>  	} while (read_seqcount_retry(&groupc->seq, seq));
>  
>  	/* Calculate state time deltas against the previous snapshot */
> @@ -280,6 +291,10 @@ 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);
>  }
>  
>  static void calc_avgs(unsigned long avg[3], int missed_periods,
  

On Thu, Oct 27, 2022 at 11:50 PM Chengming Zhou
<zhouchengming@bytedance.com> wrote:
>
> Hello,
>
> Thanks for picking this up. There is a newer version which has been acked:
> https://lore.kernel.org/all/20221014110551.22695-1-zhouchengming@bytedance.com/

Hmm. Indeed this seems to be an older version and not the one I asked
Peter to pick up in
https://lore.kernel.org/all/CAJuCfpHeJuZBbv-q+WXjgNHwt_caMomFPL3L9rxosXOrZz3fBw@mail.gmail.com/.
Not sure what went wrong. Peter, could you please replace this one
with https://lore.kernel.org/all/20221014110551.22695-1-zhouchengming@bytedance.com/?

Chengming, please do not top-post next time. Would be better if you
posted your note under the "Link:" field in this email.
Thanks!

>
> As well another PSI patch that has been acked by Johannes:
> https://lore.kernel.org/all/20220926081931.45420-1-zhouchengming@bytedance.com/
>
> Thanks!
>
>
> On 2022/10/28 14:42, tip-bot2 for Chengming Zhou wrote:
> > The following commit has been merged into the sched/core branch of tip:
> >
> > Commit-ID:     7d89d7bb921c5ae5a428df282e64ee5692e26fe0
> > Gitweb:        https://git.kernel.org/tip/7d89d7bb921c5ae5a428df282e64ee5692e26fe0
> > Author:        Chengming Zhou <zhouchengming@bytedance.com>
> > AuthorDate:    Mon, 10 Oct 2022 18:42:06 +08:00
> > Committer:     Peter Zijlstra <peterz@infradead.org>
> > CommitterDate: Thu, 27 Oct 2022 11:01:23 +02:00
> >
> > sched/psi: Fix avgs_work re-arm in psi_avgs_work()
> >
> > 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 consider current CPU groupc as IDLE if the
> > kworker running avgs_work is the only task running and no IOWAIT
> > or MEMSTALL sleep tasks, in which case we will shut off the avgs_work
> > if other CPUs' groupc are also IDLE.
> >
> > 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@quicinc.com>
> > Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > Link: https://lore.kernel.org/r/20221010104206.12184-1-zhouchengming@bytedance.com
> > ---
> >  kernel/sched/psi.c | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> >
> > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> > index ee2ecc0..f4cdf6f 100644
> > --- a/kernel/sched/psi.c
> > +++ b/kernel/sched/psi.c
> > @@ -242,6 +242,8 @@ static void get_recent_times(struct psi_group *group, int cpu,
> >                            u32 *pchanged_states)
> >  {
> >       struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
> > +     int current_cpu = raw_smp_processor_id();
> > +     bool only_avgs_work = false;
> >       u64 now, state_start;
> >       enum psi_states s;
> >       unsigned int seq;
> > @@ -256,6 +258,15 @@ 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 for this groupc.
> > +              * Normally this kworker will sleep soon and won't wake
> > +              * avgs_work back up in psi_group_change().
> > +              */
> > +             if (current_cpu == cpu && groupc->tasks[NR_RUNNING] == 1 &&
> > +                 !groupc->tasks[NR_IOWAIT] && !groupc->tasks[NR_MEMSTALL])
> > +                     only_avgs_work = true;
> >       } while (read_seqcount_retry(&groupc->seq, seq));
> >
> >       /* Calculate state time deltas against the previous snapshot */
> > @@ -280,6 +291,10 @@ 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);
> >  }
> >
> >  static void calc_avgs(unsigned long avg[3], int missed_periods,
  

On 2022/10/28 23:58, Suren Baghdasaryan wrote:
> On Thu, Oct 27, 2022 at 11:50 PM Chengming Zhou
> <zhouchengming@bytedance.com> wrote:
>>
>> Hello,
>>
>> Thanks for picking this up. There is a newer version which has been acked:
>> https://lore.kernel.org/all/20221014110551.22695-1-zhouchengming@bytedance.com/
> 
> Hmm. Indeed this seems to be an older version and not the one I asked
> Peter to pick up in
> https://lore.kernel.org/all/CAJuCfpHeJuZBbv-q+WXjgNHwt_caMomFPL3L9rxosXOrZz3fBw@mail.gmail.com/.
> Not sure what went wrong. Peter, could you please replace this one
> with https://lore.kernel.org/all/20221014110551.22695-1-zhouchengming@bytedance.com/?

Oh, I didn't notice that email.

> 
> Chengming, please do not top-post next time. Would be better if you
> posted your note under the "Link:" field in this email.

Got it, I will do next time.

Thanks!

> Thanks!
> 
>>
>> As well another PSI patch that has been acked by Johannes:
>> https://lore.kernel.org/all/20220926081931.45420-1-zhouchengming@bytedance.com/
>>
>> Thanks!
>>
>>
>> On 2022/10/28 14:42, tip-bot2 for Chengming Zhou wrote:
>>> The following commit has been merged into the sched/core branch of tip:
>>>
>>> Commit-ID:     7d89d7bb921c5ae5a428df282e64ee5692e26fe0
>>> Gitweb:        https://git.kernel.org/tip/7d89d7bb921c5ae5a428df282e64ee5692e26fe0
>>> Author:        Chengming Zhou <zhouchengming@bytedance.com>
>>> AuthorDate:    Mon, 10 Oct 2022 18:42:06 +08:00
>>> Committer:     Peter Zijlstra <peterz@infradead.org>
>>> CommitterDate: Thu, 27 Oct 2022 11:01:23 +02:00
>>>
>>> sched/psi: Fix avgs_work re-arm in psi_avgs_work()
>>>
>>> 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 consider current CPU groupc as IDLE if the
>>> kworker running avgs_work is the only task running and no IOWAIT
>>> or MEMSTALL sleep tasks, in which case we will shut off the avgs_work
>>> if other CPUs' groupc are also IDLE.
>>>
>>> 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@quicinc.com>
>>> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>>> Link: https://lore.kernel.org/r/20221010104206.12184-1-zhouchengming@bytedance.com
>>> ---
>>>  kernel/sched/psi.c | 15 +++++++++++++++
>>>  1 file changed, 15 insertions(+)
>>>
>>> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
>>> index ee2ecc0..f4cdf6f 100644
>>> --- a/kernel/sched/psi.c
>>> +++ b/kernel/sched/psi.c
>>> @@ -242,6 +242,8 @@ static void get_recent_times(struct psi_group *group, int cpu,
>>>                            u32 *pchanged_states)
>>>  {
>>>       struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
>>> +     int current_cpu = raw_smp_processor_id();
>>> +     bool only_avgs_work = false;
>>>       u64 now, state_start;
>>>       enum psi_states s;
>>>       unsigned int seq;
>>> @@ -256,6 +258,15 @@ 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 for this groupc.
>>> +              * Normally this kworker will sleep soon and won't wake
>>> +              * avgs_work back up in psi_group_change().
>>> +              */
>>> +             if (current_cpu == cpu && groupc->tasks[NR_RUNNING] == 1 &&
>>> +                 !groupc->tasks[NR_IOWAIT] && !groupc->tasks[NR_MEMSTALL])
>>> +                     only_avgs_work = true;
>>>       } while (read_seqcount_retry(&groupc->seq, seq));
>>>
>>>       /* Calculate state time deltas against the previous snapshot */
>>> @@ -280,6 +291,10 @@ 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);
>>>  }
>>>
>>>  static void calc_avgs(unsigned long avg[3], int missed_periods,
  

On Fri, Oct 28, 2022 at 08:58:03AM -0700, Suren Baghdasaryan wrote:

> Not sure what went wrong. Peter, could you please replace this one

Probably me being an idiot and searching on subject instead of msgid :/

I'll go fix up -- tomorrow though, it's late and I'm likely to mess it
up again.
  

On Fri, Oct 28, 2022 at 09:53:57PM +0200, Peter Zijlstra wrote:
> On Fri, Oct 28, 2022 at 08:58:03AM -0700, Suren Baghdasaryan wrote:
> 
> > Not sure what went wrong. Peter, could you please replace this one
> 
> Probably me being an idiot and searching on subject instead of msgid :/
> 
> I'll go fix up -- tomorrow though, it's late and I'm likely to mess it
> up again.

Can you please check queue.git/sched/core ; did I get it right this
time?
  

On 2022/10/29 19:55, Peter Zijlstra wrote:
> On Fri, Oct 28, 2022 at 09:53:57PM +0200, Peter Zijlstra wrote:
>> On Fri, Oct 28, 2022 at 08:58:03AM -0700, Suren Baghdasaryan wrote:
>>
>>> Not sure what went wrong. Peter, could you please replace this one
>>
>> Probably me being an idiot and searching on subject instead of msgid :/
>>
>> I'll go fix up -- tomorrow though, it's late and I'm likely to mess it
>> up again.
> 
> Can you please check queue.git/sched/core ; did I get it right this
> time?

I just checked that three patches, LGTM.

And would you mind picking up this, by the way?

https://lore.kernel.org/all/20220926081931.45420-1-zhouchengming@bytedance.com/

Thanks!
  

On Sat, Oct 29, 2022 at 5:42 AM Chengming Zhou
<zhouchengming@bytedance.com> wrote:
>
> On 2022/10/29 19:55, Peter Zijlstra wrote:
> > On Fri, Oct 28, 2022 at 09:53:57PM +0200, Peter Zijlstra wrote:
> >> On Fri, Oct 28, 2022 at 08:58:03AM -0700, Suren Baghdasaryan wrote:
> >>
> >>> Not sure what went wrong. Peter, could you please replace this one
> >>
> >> Probably me being an idiot and searching on subject instead of msgid :/
> >>
> >> I'll go fix up -- tomorrow though, it's late and I'm likely to mess it
> >> up again.
> >
> > Can you please check queue.git/sched/core ; did I get it right this
> > time?
>
> I just checked that three patches, LGTM.

Yep, all three patches are correct. Thanks!

>
> And would you mind picking up this, by the way?
>
> https://lore.kernel.org/all/20220926081931.45420-1-zhouchengming@bytedance.com/
>
> Thanks!