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SubjectRe: [PATCH V6] powercap/drivers/idle_injection: Add an idle injection framework
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On 12/06/2018 14:52, Peter Zijlstra wrote:
> On Tue, Jun 12, 2018 at 02:44:29PM +0200, Daniel Lezcano wrote:
>> 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.
>
> Yes, that should all get fixed. It's mostly legacy code I suppose. It's
> been at least 10 years I think since we merged the whole
> CPUMASK_OFFSTACK stuff.
>
>> What would be the best practice ? Allocate a per cpumask at init time as
>> a temporary mask to work with ?
>
> In this case, you can do:

That is what we had before but we change the code to set the count
before waking up the task, so compute the cpumask_weight of the
resulting AND right before this loop.

> + for_each_cpu_and(cpu, &ii_dev->cpumask, cpu_online_mask) {
> + iit = per_cpu_ptr(&idle_injection_thread, cpu);
> + iit->should_run = 1;
> + wake_up_process(iit->tsk);
> + }
>


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