Messages in this thread | | | Date | Mon, 18 Jun 2018 16:08:44 +0530 | From | Viresh Kumar <> | Subject | Re: [PATCH V7] powercap/drivers/idle_injection: Add an idle injection framework |
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On 18-06-18, 12:35, Daniel Lezcano wrote: > On 18/06/2018 12:22, Viresh Kumar wrote: > > On 15-06-18, 11:19, Daniel Lezcano wrote: > >> +/** > >> + * idle_injection_stop - stops the idle injections > >> + * @ii_dev: a pointer to an idle injection_device structure > >> + * > >> + * The function stops the idle injection and waits for the threads to > >> + * complete. If we are in the process of injecting an idle cycle, then > >> + * this will wait the end of the cycle. > >> + * > >> + * When the function returns there is no more idle injection > >> + * activity. The kthreads are scheduled out and the periodic timer is > >> + * off. > >> + */ > >> +void idle_injection_stop(struct idle_injection_device *ii_dev) > >> +{ > >> + struct idle_injection_thread *iit; > >> + unsigned int cpu; > >> + > >> + pr_debug("Stopping injecting idle cycles on CPUs '%*pbl'\n", > >> + cpumask_pr_args(to_cpumask(ii_dev->cpumask))); > >> + > >> + hrtimer_cancel(&ii_dev->timer); > >> + > >> + /* > >> + * We want the guarantee we have a quescient point where > >> + * parked threads stay in there state while we are stopping > >> + * the idle injection. After exiting the loop, if any CPU is > >> + * plugged in, the 'should_run' boolean being false, the > >> + * smpboot main loop schedules the task out. > >> + */ > >> + cpu_hotplug_disable(); > >> + > >> + for_each_cpu_and(cpu, to_cpumask(ii_dev->cpumask), cpu_online_mask) { > > > > Maybe you should do below for all CPUs in the mask. Is the below usecase > > possible ? > > > > - CPU0-4 are part of the mask and are all online. > > - hrtimer fires and sets should_run for all of them to 1. > > ^^ > hrtimer_cancel gives you the guarantee, the timer is no longer active > and there is no execution in the timer handler. So the timer can no > longer fire after hrtimer_cancel() is called (which is a blocking call).
Right but that isn't called yet in my sequence.
> > - Right at this time CPU3 goes offline, so the thread gets parked with > > should_run == 1. Is there a reason why this can't happen ? > > - Now we unregister the stuff and CPU3 again comes online.
It gets called here from unregister/stop.
> > - Because it had should_run as true, we again run the thread and Crash. > > > > makes sense ?
> >> +out_rollback_per_cpu: > >> + for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) > >> + per_cpu(idle_injection_device, cpu) = NULL; > > > > So if two parts of the kernel call this routine with the same cpumask, then the > > second call will also overwrite the masks with NULL and return error. That will > > screw up things a bit here. > > Apparently there is a misunderstanding :) > > https://lkml.org/lkml/2018/5/29/209 (at the end)
Right, your earlier version was doing the right thing :)
-- viresh
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