linux-kernel - Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load

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Message-ID: <56F95D10.4070400@linaro.org>
Date:	Mon, 28 Mar 2016 09:34:24 -0700
From:	Steve Muckle <steve.muckle@...aro.org>
To:	Dietmar Eggemann <dietmar.eggemann@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Juri Lelli <Juri.Lelli@....com>,
	Patrick Bellasi <patrick.bellasi@....com>,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [PATCH 1/2] sched/fair: move cpufreq hook to
 update_cfs_rq_load_avg()

Hi Dietmar,

On 03/28/2016 05:02 AM, Dietmar Eggemann wrote:
> Hi Steve,
> 
> these patches fall into the bucket of 'optimization of updating the
> value only if the root cfs_rq util has changed' as discussed in '[PATCH
> 5/8] sched/cpufreq: pass sched class into cpufreq_update_util' of Mike
> T's current series '[PATCH 0/8] schedutil enhancements', right?

I would say just the second patch is an optimization. The first and
third patches cover additional paths in CFS where the hook should be
called but currently is not, which I think is a correctness issue.

> I wonder if it makes sense to apply them before a proper 'capacity vote
> aggregation from CFS/RT/DL' has been agreed upon?

Getting the right call sites for the hook in CFS should be orthogonal to
the sched class vote aggregation IMO.

> Otherwise I agree with the changes in your 3 patches (inc. "[RFC PATCH]
> sched/fair: call cpufreq hook in additional paths") to only invoke
> cpufreq_update_util() if &rq->cfs.avg.util_avg has really changed.
> 
> 
> On 03/22/2016 01:21 AM, Steve Muckle wrote:
>> The cpufreq hook should be called whenever the root cfs_rq
>> utilization changes so update_cfs_rq_load_avg() is a better
>> place for it. The current location is not invoked in the
>> enqueue_entity() or update_blocked_averages() paths.
>>
>> Suggested-by: Vincent Guittot <vincent.guittot@...aro.org>
>> Signed-off-by: Steve Muckle <smuckle@...aro.org>
>> ---
>>   kernel/sched/fair.c | 50
>> ++++++++++++++++++++++++++------------------------
>>   1 file changed, 26 insertions(+), 24 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 46d64e4ccfde..d418deb04049 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -2825,7 +2825,9 @@ static inline u64 cfs_rq_clock_task(struct
>> cfs_rq *cfs_rq);
>>   static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq
>> *cfs_rq)
>>   {
>>       struct sched_avg *sa = &cfs_rq->avg;
>> +    struct rq *rq = rq_of(cfs_rq);
>>       int decayed, removed = 0;
>> +    int cpu = cpu_of(rq);
>>
>>       if (atomic_long_read(&cfs_rq->removed_load_avg)) {
>>           s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
>> @@ -2840,7 +2842,7 @@ static inline int update_cfs_rq_load_avg(u64
>> now, struct cfs_rq *cfs_rq)
>>           sa->util_sum = max_t(s32, sa->util_sum - r * LOAD_AVG_MAX, 0);
>>       }
>>
>> -    decayed = __update_load_avg(now, cpu_of(rq_of(cfs_rq)), sa,
>> +    decayed = __update_load_avg(now, cpu, sa,
>>           scale_load_down(cfs_rq->load.weight), cfs_rq->curr != NULL,
>> cfs_rq);
> 
> Why did you change these 3 lines above? You reverted this back in "[RFC
> PATCH] sched/fair: call cpufreq hook in additional paths".

If all three patches are accepted in principle I can restructure them if
so desired. I did not want to introduce a dependency between them and
patch 2 represents the cleanest implementation at that point.

Thanks for the review!

thanks,
Steve