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From:   Valentin Schneider <valentin.schneider@arm.com>
To:     Vincent Guittot <vincent.guittot@linaro.org>, mingo@redhat.com,
        peterz@infradead.org, juri.lelli@redhat.com,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org,
        joel@joelfernandes.org
Cc:     fweisbec@gmail.com, tglx@linutronix.de, qais.yousef@arm.com,
        Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [PATCH 7/7 v3] sched/fair: reduce the window for duplicated update
In-Reply-To: <20210212141744.24284-8-vincent.guittot@linaro.org>
References: <20210212141744.24284-1-vincent.guittot@linaro.org> <20210212141744.24284-8-vincent.guittot@linaro.org>
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Date:   Fri, 12 Feb 2021 19:19:58 +0000
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On 12/02/21 15:17, Vincent Guittot wrote:
> Start to update last_blocked_load_update_tick to reduce the possibility
> of another cpu starting the update one more time
>

IIUC this can happen if e.g. a CPU is busy updating load in
update_blocked_averages() while another enters update_nohz_stats() for the
same rq. They'll be serialized by the RQ lock, but both can still enter
update_blocked_averages() at roughly the same time.

Shouldn't then the rq->last_blocked_load_update_tick check be either
deferred to or re-done within update_blocked_averages(), with the rq lock
held?