linux-kernel - Re: [PATCH v14 1/6] sched/core: uclamp: Extend CPU's cgroup controller

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Date:   Fri, 30 Aug 2019 11:45:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-api@...r.kernel.org, cgroups@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Paul Turner <pjt@...gle.com>, Michal Koutny <mkoutny@...e.com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Alessio Balsini <balsini@...roid.com>
Subject: Re: [PATCH v14 1/6] sched/core: uclamp: Extend CPU's cgroup
 controller

On Thu, Aug 22, 2019 at 02:28:06PM +0100, Patrick Bellasi wrote:
> +#define _POW10(exp) ((unsigned int)1e##exp)
> +#define POW10(exp) _POW10(exp)

What is this magic? You're forcing a float literal into an integer.
Surely that deserves a comment!

> +struct uclamp_request {
> +#define UCLAMP_PERCENT_SHIFT	2
> +#define UCLAMP_PERCENT_SCALE	(100 * POW10(UCLAMP_PERCENT_SHIFT))
> +	s64 percent;
> +	u64 util;
> +	int ret;
> +};
> +
> +static inline struct uclamp_request
> +capacity_from_percent(char *buf)
> +{
> +	struct uclamp_request req = {
> +		.percent = UCLAMP_PERCENT_SCALE,
> +		.util = SCHED_CAPACITY_SCALE,
> +		.ret = 0,
> +	};
> +
> +	buf = strim(buf);
> +	if (strncmp("max", buf, 4)) {

That is either a bug, and you meant to write: strncmp(buf, "max", 3), or
it is not, and then you could've written: strcmp(buf, "max")

But as written it doesn't make sense.

> +		req.ret = cgroup_parse_float(buf, UCLAMP_PERCENT_SHIFT,
> +					     &req.percent);
> +		if (req.ret)
> +			return req;
> +		if (req.percent > UCLAMP_PERCENT_SCALE) {
> +			req.ret = -ERANGE;
> +			return req;
> +		}
> +
> +		req.util = req.percent << SCHED_CAPACITY_SHIFT;
> +		req.util = DIV_ROUND_CLOSEST_ULL(req.util, UCLAMP_PERCENT_SCALE);
> +	}
> +
> +	return req;
> +}