Re: [PATCH 1/6] cpufreq: schedutil: reset sg_cpus's flags at IDLE enter

Steven Rostedt
2017-03-06T14:32:10Z

On Fri, 3 Mar 2017 09:11:25 +0530
Viresh Kumar <viresh.kumar@linaro.org> wrote:

> On 02-03-17, 15:45, Patrick Bellasi wrote:
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index e2ed46d..739b29d 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -3653,6 +3653,7 @@ static inline unsigned long rlimit_max(unsigned int limit)
> > #define SCHED_CPUFREQ_RT (1U << 0)
> > #define SCHED_CPUFREQ_DL (1U << 1)
> > #define SCHED_CPUFREQ_IOWAIT (1U << 2)
> > +#define SCHED_CPUFREQ_IDLE (1U << 3)
> >
> > #define SCHED_CPUFREQ_RT_DL (SCHED_CPUFREQ_RT | SCHED_CPUFREQ_DL)
> >
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index fd46593..084a98b 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -281,6 +281,12 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
> >
> > raw_spin_lock(&sg_policy->update_lock);
> >
> > + /* CPU is entering IDLE, reset flags without triggering an update */
> > + if (flags & SCHED_CPUFREQ_IDLE) {
>
> Will "flags == SCHED_CPUFREQ_IDLE" generate better assembly ?
>

Even if it does, a bit check and an equal check are pretty negligible
in difference wrt execution time. I would choose whatever is the most
readable to humans.

flags == SCHED_CPUFREQ_IDLE

will tell me (as a reviewer) that we expect no other flag to be set.

flags & SCHED_CPUFREQ_IDLE

will tell me that we only care about the IDLE flag.

Which ever is the more meaningful is what should be used.

-- Steve

> > + sg_cpu->flags = 0;
> > + goto done;
> > + }
> > +
> > sg_cpu->util = util;
> > sg_cpu->max = max;
> > sg_cpu->flags = flags;
> > @@ -293,6 +299,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
> > sugov_update_commit(sg_policy, time, next_f);
> > }
> >
> > +done:
> > raw_spin_unlock(&sg_policy->update_lock);
> > }
> >
> > diff --git a/kernel/sched/idle_task.c b/kernel/sched/idle_task.c
> > index 0c00172..a844c91 100644
> > --- a/kernel/sched/idle_task.c
> > +++ b/kernel/sched/idle_task.c
> > @@ -29,6 +29,10 @@ pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
> > put_prev_task(rq, prev);
> > update_idle_core(rq);
> > schedstat_inc(rq->sched_goidle);
> > +
> > + /* kick cpufreq (see the comment in kernel/sched/sched.h). */
> > + cpufreq_update_this_cpu(rq, SCHED_CPUFREQ_IDLE);
> > +
> > return rq->idle;
> > }
> >
> > --
> > 2.7.4
>