Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Sat, 16 Dec 2017 17:40:00 +0100 | Subject | Re: [PATCH 2/4] sched: cpufreq: Keep track of cpufreq utilization update flags |
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On Wed, Dec 13, 2017 at 10:53 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: > Currently the schedutil governor overwrites the sg_cpu->flags field on > every call to the utilization handler. It was pretty good as the initial > implementation of utilization handlers, there are several drawbacks > though. > > The biggest drawback is that the sg_cpu->flags field doesn't always > represent the correct type of tasks that are enqueued on a CPU's rq. For > example, if a fair task is enqueued while a RT or DL task is running, we > will overwrite the flags with value 0 and that may take the CPU to lower > OPPs unintentionally. There can be other corner cases as well which we > aren't aware of currently. > > This patch changes the current implementation to keep track of all the > task types that are currently enqueued to the CPUs rq. A new flag: CLEAR > is introduced and is set by the scheduling classes when their last task > is dequeued. When the CLEAR flag bit is set, the schedutil governor resets > all the other flag bits that are present in the flags parameter. For > now, the util update handlers return immediately if they were called to > clear the flag. > > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> > --- > include/linux/sched/cpufreq.h | 7 ++++++- > kernel/sched/cpufreq_schedutil.c | 21 ++++++++++++++++++--- > kernel/sched/deadline.c | 4 ++++ > kernel/sched/fair.c | 8 ++++++-- > kernel/sched/rt.c | 4 ++++ > 5 files changed, 38 insertions(+), 6 deletions(-) > > diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h > index d1ad3d825561..6f6641e61236 100644 > --- a/include/linux/sched/cpufreq.h > +++ b/include/linux/sched/cpufreq.h > @@ -8,10 +8,15 @@ > * Interface between cpufreq drivers and the scheduler: > */ > > +#define SCHED_CPUFREQ_CLEAR (1U << 31)
I'm not thrilled by this, because schedutil is not the only user of the flags and it's totally unclear what the other user(s) should do when this is set.
Thanks, Rafael
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