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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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