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From:   Valentin Schneider <valentin.schneider@arm.com>
To:     Qais Yousef <qais.yousef@arm.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Patrick Bellasi <patrick.bellasi@matbug.net>,
        Chris Redpath <chris.redpath@arm.com>,
        Lukasz Luba <lukasz.luba@arm.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/2] sched/uclamp: Fix initialization of strut uclamp_rq
In-reply-to: <20200624172605.26715-2-qais.yousef@arm.com>
Date:   Thu, 25 Jun 2020 01:09:54 +0100
Message-ID: <jhj7dvwrood.mognet@arm.com>
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On 24/06/20 18:26, Qais Yousef wrote:
> struct uclamp_rq was zeroed out entirely in assumption that in the first
> call to uclamp_rq_inc() they'd be initialized correctly in accordance to
> default settings.
>
> But when next patch introduces a static key to skip
> uclamp_rq_{inc,dec}() until userspace opts in to use uclamp, schedutil
> will fail to perform any frequency changes because the
> rq->uclamp[UCLAMP_MAX].value is zeroed at init and stays as such. Which
> means all rqs are capped to 0 by default.
>
> Fix it by making sure we do proper initialization at init without
> relying on uclamp_rq_inc() doing it later.
>
> Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
> Signed-off-by: Qais Yousef <qais.yousef@arm.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> CC: Patrick Bellasi <patrick.bellasi@matbug.net>
> Cc: Chris Redpath <chris.redpath@arm.com>
> Cc: Lukasz Luba <lukasz.luba@arm.com>
> Cc: linux-kernel@vger.kernel.org

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>