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

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Date:   Tue, 12 Jun 2018 14:44:29 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     viresh.kumar@...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 12/06/2018 14:30, Peter Zijlstra wrote:
> On Tue, Jun 12, 2018 at 02:00:11PM +0200, Daniel Lezcano wrote:
>> +static void __idle_injection_wakeup(struct idle_injection_device *ii_dev)
>> +{
>> +	struct idle_injection_thread *iit;
>> +	struct cpumask tmp;
>> +	unsigned int cpu;
>> +
>> +	cpumask_and(&tmp, ii_dev->cpumask, cpu_online_mask);
> 
> You should not be having a cpumask on the stack. Those things can be
> ginormous.

Ok, the kernel code uses of cpumask_t on the stack when dealing with
cpumask_and. I assume it is also not recommended.

What would be the best practice ? Allocate a per cpumask at init time as
a temporary mask to work with ?




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