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;
Date:   Thu, 16 Apr 2020 13:41:31 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     Quentin Perret <qperret@google.com>, mingo@redhat.com,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        ctheegal@codeaurora.org, dianders@chromium.org,
        patrick.bellasi@matbug.net, valentin.schneider@arm.com,
        qais.yousef@arm.com, linux-kernel@vger.kernel.org,
        kernel-team@android.com
Subject: Re: [PATCH v2] sched/core: Fix reset-on-fork from RT with uclamp
Message-ID: <20200416114131.GO20730@hirez.programming.kicks-ass.net>
References: <20200416085956.217587-1-qperret@google.com>
 <cf82cb73-b837-2365-9178-d56589c3ad44@arm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <cf82cb73-b837-2365-9178-d56589c3ad44@arm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Apr 16, 2020 at 01:03:16PM +0200, Dietmar Eggemann wrote:
> On 16.04.20 10:59, Quentin Perret wrote:
> > uclamp_fork() resets the uclamp values to their default when the
> > reset-on-fork flag is set. It also checks whether the task has a RT
> > policy, and sets its uclamp.min to 1024 accordingly. However, during
> > reset-on-fork, the task's policy is lowered to SCHED_NORMAL right after,
> > hence leading to an erroneous uclamp.min setting for the new task if it
> > was forked from RT.
> > 
> > Fix this by removing the unnecessary check on rt_task() in
> > uclamp_fork() as this doesn't make sense if the reset-on-fork flag is
> > set.
> > 
> > Fixes: 1a00d999971c ("sched/uclamp: Set default clamps for RT tasks")
> > Reported-by: Chitti Babu Theegala <ctheegal@codeaurora.org>
> > Reviewed-by: Patrick Bellasi <patrick.bellasi@matbug.net>
> > Signed-off-by: Quentin Perret <qperret@google.com>
> > ---
> > Changes in v2:
> >  - Added missing 'Fixes:' tag (Patrick)
> >  - Removed unnecessary local variable (Doug, Patrick)
> > ---
> >  kernel/sched/core.c | 9 ++-------
> >  1 file changed, 2 insertions(+), 7 deletions(-)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 3a61a3b8eaa9..9a2fbf98fd6f 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1232,13 +1232,8 @@ static void uclamp_fork(struct task_struct *p)
> >  		return;
> >  
> >  	for_each_clamp_id(clamp_id) {
> > -		unsigned int clamp_value = uclamp_none(clamp_id);
> > -
> > -		/* By default, RT tasks always get 100% boost */
> > -		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
> > -			clamp_value = uclamp_none(UCLAMP_MAX);
> > -
> > -		uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
> > +		uclamp_se_set(&p->uclamp_req[clamp_id],
> > +			      uclamp_none(clamp_id), false);
> >  	}
> >  }
> 
> LGTM.
> 
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

Thanks guys!