Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg()

From: Dietmar Eggemann
Date: Mon Mar 28 2016 - 09:35:06 EST

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

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@xxxxxxxxxx>
Signed-off-by: Steve Muckle <smuckle@xxxxxxxxxx>
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".