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

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Date:   Fri, 2 Jun 2023 13:57:18 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Aaron Tomlin <atomlin@...mlin.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 2/4] vmstat: skip periodic vmstat update for nohz full
 CPUs

On Fri, Jun 02, 2023 at 12:39:04PM +0200, Michal Hocko wrote:
> 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?

Changed to cpu_is_isolated, thanks.