Re: [PATCH 2/4] vmstat: skip periodic vmstat update for nohz full CPUs

[Michal Hocko]

On Tue 30-05-23 11:52:36, Marcelo Tosatti wrote:
> @@ -2022,6 +2023,16 @@ static void vmstat_shepherd(struct work_
>  	for_each_online_cpu(cpu) {
>  		struct delayed_work *dw = &per_cpu(vmstat_work, cpu);
>  
> +		/*
> +		 * Skip periodic updates for nohz full CPUs.
> +		 * Any callers who need precise values should use
> +		 * a snapshot of the per-CPU counters, or use the global
> +		 * counters with measures to handle errors up to
> +		 * thresholds (see calculate_normal_threshold).
> +		 */
> +		if (tick_nohz_full_cpu(cpu))
> +			continue;

In other code path we have used cpu_is_isolated, is there any reason to
diverge from that here? Isn't this effectivelly the same kind of
problem?

> +
>  		if (!delayed_work_pending(dw) && need_update(cpu))
>  			queue_delayed_work_on(cpu, mm_percpu_wq, dw, 0);
>  
> 

-- 
Michal Hocko
SUSE Labs