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From:   Valentin Schneider <valentin.schneider@arm.com>
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Qais Yousef <qais.yousef@arm.com>
Subject: Re: [PATCH 0/7 v4] move update blocked load outside newidle_balance
In-Reply-To: <CAKfTPtDjVBP676kzW-5QF8nMyD1+WNnJWH4=gKPVV+55tm3Cng@mail.gmail.com>
References: <20210224133007.28644-1-vincent.guittot@linaro.org> <jhjblc95mo0.mognet@arm.com> <CAKfTPtDjVBP676kzW-5QF8nMyD1+WNnJWH4=gKPVV+55tm3Cng@mail.gmail.com>
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Date:   Thu, 25 Feb 2021 12:14:37 +0000
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On 25/02/21 09:05, Vincent Guittot wrote:
>> One last thing for patch 7: mayhaps we could do a tad better to avoid
>> duplicate updates going through a heapful of leaf cfs rqs, see
>>
>>   http://lore.kernel.org/r/jhj4kiht7oh.mognet@arm.com
>
> rq->last_blocked_load_update_tick is there only to filter duplicate
> update during _nohz_idle_balance but not for other normal LB.
>

Right, update_nohz_stats() is now only used in _nohz_idle_balance()...
IIUC the pattern being covered here would be a CPUX getting kicked for nohz
stats/balance, then some CPUX-N (so it gets picked by find_new_ilb())
entering idle and getting kick in turn (less than a jiffy apart).