linux-kernel - Re: [PATCH V6] powercap/drivers/idle_injection: Add an idle injection framework

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Date:   Wed, 13 Jun 2018 13:54:31 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>, rjw@...ysocki.net,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Eduardo Valentin <edubezval@...il.com>,
        Javi Merino <javi.merino@...nel.org>,
        Leo Yan <leo.yan@...aro.org>,
        Kevin Wangtao <kevin.wangtao@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rui Zhang <rui.zhang@...el.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Andrea Parri <andrea.parri@...rulasolutions.com>
Subject: Re: [PATCH V6] powercap/drivers/idle_injection: Add an idle
 injection framework

On 12-06-18, 14:59, Peter Zijlstra wrote:
> On Tue, Jun 12, 2018 at 02:00:11PM +0200, Daniel Lezcano wrote:
> > +struct idle_injection_device {
> 
> remove this:
> > +	cpumask_var_t cpumask;
> 
> > +	struct hrtimer timer;
> > +	struct completion stop_complete;
> > +	unsigned int idle_duration_ms;
> > +	unsigned int run_duration_ms;
> > +	atomic_t count;
> 
> add:
> 	unsigned long cpumask[0];
> > +};
> 
> 
> > +static struct idle_injection_device *ii_dev_alloc(void)
> > +{
> > +	struct idle_injection_device *ii_dev;
> > +
> > +	ii_dev = kzalloc(sizeof(*ii_dev), GFP_KERNEL);
> 
> use:
> 
> 	sizeof(*ii_dev) + cpumask_size()
> 
> > +	if (!ii_dev)
> > +		return NULL;
> > +
> 
> delete:
> 
> > +	if (!alloc_cpumask_var(&ii_dev->cpumask, GFP_KERNEL)) {
> > +		kfree(ii_dev);
> > +		return NULL;
> > +	}
> > +
> > +	return ii_dev;
> > +}
> 
> And use:
> 
> 	to_cpumask(ii_dev->cpumask)

What's the benefit of these changes? Is it just about not allocating memory
twice or more than that ?

And what could we do in situations where we need two cpumask variables (we have
a case in cpufreq core for that) ?

-- 
viresh