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Date:   Fri, 2 Jun 2023 12:39:04 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Marcelo Tosatti <mtosatti@redhat.com>
Cc:     Christoph Lameter <cl@linux.com>,
        Aaron Tomlin <atomlin@atomlin.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH 2/4] vmstat: skip periodic vmstat update for nohz full
 CPUs
Message-ID: <ZHnGyNd4lHz/pwKr@dhcp22.suse.cz>
References: <20230530145234.968927611@redhat.com>
 <20230530145335.828634764@redhat.com>
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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