Re: [PATCH v6 2/2] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too

[Aaron Tomlin]

On Tue 2022-08-16 15:11 -0300, Marcelo Tosatti wrote:
> Aaron,
> 
> It is also necessary to remove the delayed_work_pending check from
> quiet_vmstat:
> 
> @@ -1987,10 +1970,7 @@ void quiet_vmstat(void)
>         if (system_state != SYSTEM_RUNNING)
>                 return;
>  
> -       if (!delayed_work_pending(this_cpu_ptr(&vmstat_work)))
> -               return;
> -
> -       if (!need_update(smp_processor_id()))
> +       if (!__this_cpu_read(vmstat_dirty))
>                 return;
>  
> 
> Because, consider the following situation:
> 
> 
> vmstat_shepherd CPU				nohz_full CPU
> 
> 						
> 						vmstat_dirty = false
> 						enter nohz_full
> 						return to userspace
> check vmstat_dirty, unset,
> delayed work cancelled.
> 						dirties per-CPU vmstats
> 						vmstat_dirty = true
> 						return to userspace
> 						(quiet_vmstat will skip
> 						 clearing stats because
> 						 delayed work was not queued).

Hi Marcelo,

Yes, I agree - the above scenario can occur.


Kind regards,

-- 
Aaron Tomlin