Messages in this thread | | | Subject | Re: [PATCH V5] powercap/drivers/idle_injection: Add an idle injection framework | From | Daniel Lezcano <> | Date | Wed, 6 Jun 2018 12:22:07 +0200 |
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On 06/06/2018 06:27, Viresh Kumar wrote: > On 05-06-18, 16:54, Daniel Lezcano wrote: >> On 05/06/2018 12:39, Viresh Kumar wrote: >> I don't think you are doing a mistake. Even if this can happen >> theoretically, I don't think practically that is the case. >> >> The play_idle() has 1ms minimum sleep time. >> >> The scenario you are describing means: >> >> 1. the loop in idle_injection_wakeup() takes more than 1ms to achieve > > There are many ways in which idle_injection_wakeup() can get called. > > - from hrtimer handler, this happens in softirq context, right? So interrupts > can still block the handler to run ? > > - from idle_injection_start(), process context. RT or DL or IRQ activity can > block the CPU for long durations sometimes. > >> 2. at the same time, the user of the idle injection unregisters while >> the idle injection is acting precisely at CPU0 and exits before another >> task was wakeup by the loop in 1. more than 1ms after. >> >> >From my POV, this scenario can't happen. > > Maybe something else needs to be buggy as well to make this crap happen. > >> Anyway, we must write rock solid code > > That's my point. > >> so may be we can use a refcount to >> protect against that, so instead of freeing in unregister, we refput the >> ii_dev pointer. > > I think the solution can be a simple change in implementation of > idle_injection_wakeup(), something like this.. > > +static void idle_injection_wakeup(struct idle_injection_device *ii_dev) > +{ > + struct idle_injection_thread *iit; > + int cpu; > + > + for_each_cpu_and(cpu, ii_dev->cpumask, cpu_online_mask) > + atomic_inc(&ii_dev->count); > > + > + mb(); //I am not sure but I think we need some kind of barrier here ?
(mb() are done in the atomic operations AFAICT).
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(); ?
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.
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