linux-kernel - Re: [PATCH 3/3] sched/fair: Consider uclamp for "task fits capacity" checks

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Message-ID: <20191124222051.kbb62phfsln5ixg4@e107158-lin.cambridge.arm.com>
Date:   Sun, 24 Nov 2019 22:20:52 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...nel.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, patrick.bellasi@...bug.net,
        qperret@...gle.com, morten.rasmussen@....com
Subject: Re: [PATCH 3/3] sched/fair: Consider uclamp for "task fits capacity"
 checks

On 11/20/19 17:55, Valentin Schneider wrote:
> +static inline
> +unsigned long uclamp_task_util(struct task_struct *p, unsigned long util)
> +{
> +	return clamp(util,
> +		     (unsigned long)uclamp_eff_value(p, UCLAMP_MIN),
> +		     (unsigned long)uclamp_eff_value(p, UCLAMP_MAX));
> +}

uclamp_eff_value() will check if a task belongs to a cgroup, and if it does
apply its uclamp. The funny thing about the cgroup settings is that they can
have a uclamp_max < uclamp_min. uclamp_util_with() does check for this
condition but this function doesn't.

I would prefer to teach uclamp_util_with() to accept a NULL rq argument, then
we can have 2 convenient function uclamp_rq_util() and uclamp_task_util() that
are just simple wrappers around it. It'd would be a lot better to keep the
intelligence of dealing with the correct details of clamping in a single
function IMO.

Cheers

--
Qais Yousef