On 06/06/2018 12:45, Viresh Kumar wrote:
> 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 :)
We won't be able to call completion() in this case.
--
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog
