Messages in this thread | | | Date | Wed, 10 Feb 2016 04:09:33 +0100 | Subject | Re: [PATCH 0/3] cpufreq: Replace timers with utilization update callbacks | From | "Rafael J. Wysocki" <> |
| |
On Wed, Feb 10, 2016 at 2:57 AM, Rafael J. Wysocki <rafael@kernel.org> wrote: > On Wed, Feb 10, 2016 at 2:02 AM, Steve Muckle <steve.muckle@linaro.org> wrote: >> On 02/09/2016 12:05 PM, Rafael J. Wysocki wrote: >>>>> One concern I had was, given that the lone scheduler update hook is in >>>>> CFS, is it possible for governor updates to be stalled due to RT or DL >>>>> task activity? >>>> >>>> I don't think they may be completely stalled, but I'd prefer Peter to >>>> answer that as he suggested to do it this way. >>> >>> In any case, if that concern turns out to be significant in practice, it may >>> be addressed like in the appended modification of patch [1/3] from the $subject >>> series. >>> >>> With that things look like before from the cpufreq side, but the other sched >>> classes also get a chance to trigger a cpufreq update. The drawback is the >>> cpu_clock() call instead of passing the time value from update_load_avg(), but >>> I guess we can live with that if necessary. >>> >>> FWIW, this modification doesn't seem to break things on my test machine. >>> >> ... >>> Index: linux-pm/kernel/sched/rt.c >>> =================================================================== >>> --- linux-pm.orig/kernel/sched/rt.c >>> +++ linux-pm/kernel/sched/rt.c >>> @@ -2212,6 +2212,9 @@ static void task_tick_rt(struct rq *rq, >>> >>> update_curr_rt(rq); >>> >>> + /* Kick cpufreq to prevent it from stalling. */ >>> + cpufreq_kick(); >>> + >>> watchdog(rq, p); >>> >>> /* >>> Index: linux-pm/kernel/sched/deadline.c >>> =================================================================== >>> --- linux-pm.orig/kernel/sched/deadline.c >>> +++ linux-pm/kernel/sched/deadline.c >>> @@ -1197,6 +1197,9 @@ static void task_tick_dl(struct rq *rq, >>> { >>> update_curr_dl(rq); >>> >>> + /* Kick cpufreq to prevent it from stalling. */ >>> + cpufreq_kick(); >>> + >>> /* >>> * Even when we have runtime, update_curr_dl() might have resulted in us >>> * not being the leftmost task anymore. In that case NEED_RESCHED will >> >> I think additional hooks such as enqueue/dequeue would be needed in >> RT/DL. The task tick callbacks will only run if a task in that class is >> executing at the time of the tick. There could be intermittent RT/DL >> task activity in a frequency domain (the only task activity there, no >> CFS tasks) that doesn't happen to overlap the tick. Worst case the task >> activity could be periodic in such a way that it never overlaps the tick >> and the update is never made. > > So if I'm reading this correctly, it would be better to put the hooks > into update_curr_rt/dl()?
If done this way, I guess we may pass rq_clock_task(rq) as the time arg to cpufreq_update_util() from there and then the cpu_lock() call I've added to this prototype won't be necessary any more.
Thanks, Rafael
| |