On Tue, Jun 12, 2018 at 07:02:57PM +0200, Daniel Lezcano wrote: > Mmh, it is unclear for me if the park() vs wakeup() can happen at the > same time. > > If the park() function is called, that means the hotplug is allowed.
No, it means we're inside hot-un-plug, but that doesn't stop the hrtimer from firing. > If the hotplug is allowed, we can modify the online mask. > > What happens with the online mask when we are processing it in an > interrupt context ? RCU-like, if you observe a CPU in the online mask, it will stay available, but the bit might get cleared. > > Maybe avoid the issue entire by having a > > {period,idle} tuple, where your old run := period - idle. > > Can you elaborate ? I don't get it. Have a period parameter that specifies the interval in which you have one injected idle, and specify for how long you want to inject idle; then obviously idle < period. > >>> 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.. > > Ok, do you prefer to see the timer set in the wakeup function and thus > having a periodic tick for the idle injection ? I think having a HRTIMER_RESTART handler that does hrtimer_forward() is the most sensible. You will end up having to deal with threads not being ready, but I think that's not a real problem.