Re: [PATCH V5] powercap/drivers/idle_injection: Add an idle injection framework
From: Viresh Kumar
Date: Wed Jun 06 2018 - 06:45:37 EST
On 06-06-18, 12:22, Daniel Lezcano wrote:
> (mb() are done in the atomic operations AFAICT).
AFAIU, it is required to make sure the operations are seen in a particular order
on another CPU and the compiler doesn't reorganize code to optimize it.
For example, in our case what if the compiler reorganizes the atomic-set
operation after wakeup-process ? But maybe that wouldn't happen across function
calls and we should be safe then.
> What about:
>
> get_online_cpus();
>
> nr_tasks = cpumask_weight(
> cpumask_and(ii_dev->cpumask, cpu_online_mask);
>
> atomic_set(&ii_dev->count, nr_tasks);
>
> 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);
> }
>
> put_online_cpus();
> ?
Looks good this time.
> I'm wondering if we can have a CPU hotplugged right after the
> 'put_online_cpus', resulting in the 'should park' flag set and then the
> thread goes in the kthread_parkme instead of jumping back the idle
> injection function and decrease the count, leading up to the timer not
> being set again.
True. That looks like a valid problem to me as well.
What about starting the hrtimer right from this routine itself, after taking
into account running-time, idle-time, delay, etc ? That would get rid of the
count stuff, this get_online_cpus(), etc.
Even if we restart the next play-idle cycle a bit early or with some delay, sky
wouldn't fall :)
--
viresh