Messages in this thread | | | Date | Mon, 10 Oct 2022 16:30:36 +0800 | Subject | Re: PSI idle-shutoff | From | Chengming Zhou <> |
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On 2022/10/10 14:57, Chengming Zhou wrote: > On 2022/10/10 14:43, Pavan Kondeti wrote: >> 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? > > Yes, I think you're correct, we should check !NR_IOWAIT && !NR_MEMSTALL too. >
Hello,
Looks like this patch plus the !NR_IOWAIT && !NR_MEMSTALL condition can solve the avgs_work re-arm problem.
Real machine is hard to reproduce, so I set up a QEMU VM with only one CPU and hack PSI_FREQ=100ms, with "cgroup_disable=pressure" cmdline to disable cgroup levels PSI.
After launching the VM, I ssh into it and enable some tracepoints, then exit to let it idle.
<idle>-0 [000] d..1. 77.102839: cpu_idle: state=1 cpu_id=0 <idle>-0 [000] d.s2. 77.142840: workqueue_queue_work: work struct=00000000cd023738 function=psi_avgs_work workqueue=events req_cpu=512 cpu=0 <idle>-0 [000] d.s2. 77.142841: workqueue_activate_work: work struct 00000000cd023738 <idle>-0 [000] dNs5. 77.142849: sched_wakeup: comm=kworker/0:5 pid=164 prio=120 target_cpu=000 <idle>-0 [000] dNs2. 77.142852: timer_start: timer=00000000f41058a8 function=tcp_orphan_update expires=4294744860 [timeout=100] cpu=0 idx=100 flags=D <idle>-0 [000] .N.1. 77.142854: cpu_idle: state=4294967295 cpu_id=0 <idle>-0 [000] d..2. 77.142860: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=kworker/0:5 next_pid=164 next_prio=120 kworker/0:5-164 [000] ..... 77.142864: workqueue_execute_start: work struct 00000000cd023738: function psi_avgs_work kworker/0:5-164 [000] ..... 77.142866: workqueue_execute_end: work struct 00000000cd023738: function psi_avgs_work
[avgs_work won't be re-armed again]
kworker/0:5-164 [000] d..2. 77.142872: sched_switch: prev_comm=kworker/0:5 prev_pid=164 prev_prio=120 prev_state=I ==> next_comm=swapper/0 next_pid=0 next_prio=120 <idle>-0 [000] d..1. 77.142878: cpu_idle: state=1 cpu_id=0
[avgs_work kworker sleep, won't wake_clock]
<idle>-0 [000] dNs4. 77.470857: sched_wakeup: comm=jbd2/vda3-8 pid=73 prio=120 target_cpu=000
[new activity again, avgs_work scheduled delay PSI_FREQ=100ms ...]
<idle>-0 [000] d.s2. 77.574816: workqueue_queue_work: work struct=00000000cd023738 function=psi_avgs_work workqueue=events req_cpu=512 cpu=0 <idle>-0 [000] d.s2. 77.574817: workqueue_activate_work: work struct 00000000cd023738 <idle>-0 [000] dNs5. 77.574824: sched_wakeup: comm=kworker/0:5 pid=164 prio=120 target_cpu=000 <idle>-0 [000] dNs2. 77.574826: timer_start: timer=00000000f41058a8 function=tcp_orphan_update expires=4294745292 [timeout=100] cpu=0 idx=90 flags=D <idle>-0 [000] .N.1. 77.574827: cpu_idle: state=4294967295 cpu_id=0 <idle>-0 [000] d..2. 77.574833: sched_switch: prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=kworker/0:5 next_pid=164 next_prio=120 kworker/0:5-164 [000] ..... 77.574837: workqueue_execute_start: work struct 00000000cd023738: function psi_avgs_work kworker/0:5-164 [000] ..... 77.574839: workqueue_execute_end: work struct 00000000cd023738: function psi_avgs_work
[avgs_work run as expected at 77.470857+100ms, then idle again, won't be re-armed]
kworker/0:5-164 [000] d..2. 77.574844: sched_switch: prev_comm=kworker/0:5 prev_pid=164 prev_prio=120 prev_state=I ==> next_comm=swapper/0 next_pid=0 next_prio=120 <idle>-0 [000] d..1. 77.574850: cpu_idle: state=1 cpu_id=0 <idle>-0 [000] d.s5. 77.606824: timer_start: timer=000000005f4b8bb9 function=delayed_work_timer_fn expires=4294745324 [timeout=100] cpu=0 idx=94 flags=I [...]
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