Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210224133007.28644-1-vincent.guittot@linaro.org> <jhjblc95mo0.mognet@arm.com>
In-Reply-To: <jhjblc95mo0.mognet@arm.com>
From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Thu, 25 Feb 2021 09:05:11 +0100
Message-ID: <CAKfTPtDjVBP676kzW-5QF8nMyD1+WNnJWH4=gKPVV+55tm3Cng@mail.gmail.com>
Subject: Re: [PATCH 0/7 v4] move update blocked load outside newidle_balance
To:     Valentin Schneider <valentin.schneider@arm.com>
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>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi Valentin,

On Wed, 24 Feb 2021 at 19:46, Valentin Schneider
<valentin.schneider@arm.com> wrote:
>
> On 24/02/21 14:30, Vincent Guittot wrote:
> > Joel reported long preempt and irq off sequence in newidle_balance because
> > of a large number of CPU cgroups in use and having to be updated. This
> > patchset moves the update outside newidle_imblance. This enables to early
> > abort during the updates in case of pending irq as an example.
> >
> > Instead of kicking a normal ILB that will wakes up CPU which is already
> > idle, patch 6 triggers the update of statistics in the idle thread of
> > the CPU before selecting and entering an idle state.
> >
> > Changes on v4:
> > - Add a dedicated bit for updating blocked load when entering idle.
> >   This simplifies the management of concurrency with kick_ilb.
> >
>
> I believe that solves the issues vs nohz balance.
>
> 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.

>
>
> Otherwise, feel free to add to the lot:
>
>   Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
>