Messages in this thread | | | Date | Tue, 12 Jun 2018 17:58:41 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH V6] powercap/drivers/idle_injection: Add an idle injection framework |
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On Tue, Jun 12, 2018 at 04:37:17PM +0200, Daniel Lezcano wrote: > On 12/06/2018 16:06, Peter Zijlstra wrote: > > On Tue, Jun 12, 2018 at 03:02:14PM +0200, Daniel Lezcano wrote: > >> On 12/06/2018 14:52, Peter Zijlstra wrote: > >>> 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); > >>> + } > > > > > > Ah, I see, but since you do: > > > > if (atomic_dec_and_test()) > > last_man() > > > > where that last_man() thing will start a timer, there is no real problem > > with doing atomic_inc() with before wake_up_process(). > > Viresh was worried about the scenario: > > https://lkml.org/lkml/2018/6/5/276
Ah, but I think you have more races, for instance look at wakeup vs park, what if wakeup sets should_run after you've just checked it?
Then you have an inc without a dec.
> > Also, last_man() uses @run_duration, but the way I read it, the timer is > > for waking things up again, this means it is in fact the sleep duration, > > no? > > No, it is the next idle injection deadline, meanwhile we let the system > continue running. > > The sleep duration is managed by another timer in play_idle().
No, that's the idle duration. Maybe avoid the issue entire by having a {period,idle} tuple, where your old run := period - idle.
> > Furthermore, should you not be using hrtimer_forward(&timer, > > idle_duration + run_duration) instead? AFAICT the current scheme is > > prone to drifting. > > (I assume you meant setting the timer in the wakeup task function). > > Yes, drifting is not an issue if that happens. This scheme is simpler > and safer than setting the timer ahead before waking up the tasks with > the risk it expires before all the tasks ended their idle cycles.
sloppy though..
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