Re: [PATCH] sched/fair: remove redundant call to cpufreq_update_util

From: Dietmar Eggemann
Date: Wed Jan 15 2020 - 15:20:53 EST


On 15/01/2020 11:20, Vincent Guittot wrote:
> With commit bef69dd87828 ("sched/cpufreq: Move the cfs_rq_util_change() call to cpufreq_update_util()")
> update_load_avg() has become the central point for calling cpufreq (not
> including the update of blocked load). This change helps to simplify
> further the number of call to cpufreq_update_util() and to remove last
> redundant ones. With update_load_avg(), we are now sure that
> cpufreq_update_util() will be called after every task attachment to a
> cfs_rq and especially after propagating this event down to the util_avg of
> the root cfs_rq, which is the level that is used by cpufreq governors like
> schedutil to set the frequency of a CPU.
>
> The SCHED_CPUFREQ_MIGRATION flag forces an early call to cpufreq when the
> migration happens in a cgroup whereas util_avg of root cfs_rq is not yet
> updated and this call is duplicated with the one that happens immediately
> after when the migration event reaches the root cfs_rq. The dedicated flag
> SCHED_CPUFREQ_MIGRATION is now useless and can be removed. The interface of
> attach_entity_load_avg() can also be simplified accordingly.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

LGTM. Doesn't this allow to get rid of the 'int flags' in
cfs_rq_util_change() as well?

8<---

kernel/sched/fair.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 328d59e8afba..f82f4fde0cd3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3110,7 +3110,7 @@ static inline void update_cfs_group(struct sched_entity *se)
}
#endif /* CONFIG_FAIR_GROUP_SCHED */

-static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
+static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq)
{
struct rq *rq = rq_of(cfs_rq);

@@ -3129,7 +3129,7 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
*
* See cpu_util().
*/
- cpufreq_update_util(rq, flags);
+ cpufreq_update_util(rq, 0);
}
}

@@ -3556,7 +3556,7 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s

add_tg_cfs_propagate(cfs_rq, se->avg.load_sum);

- cfs_rq_util_change(cfs_rq, 0);
+ cfs_rq_util_change(cfs_rq);

trace_pelt_cfs_tp(cfs_rq);
}
@@ -3577,7 +3577,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s

add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum);

- cfs_rq_util_change(cfs_rq, 0);
+ cfs_rq_util_change(cfs_rq);

trace_pelt_cfs_tp(cfs_rq);
}
@@ -3618,7 +3618,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
update_tg_load_avg(cfs_rq, 0);

} else if (decayed) {
- cfs_rq_util_change(cfs_rq, 0);
+ cfs_rq_util_change(cfs_rq);

if (flags & UPDATE_TG)
update_tg_load_avg(cfs_rq, 0);
@@ -3851,7 +3851,7 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq)

static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
{
- cfs_rq_util_change(cfs_rq, 0);
+ cfs_rq_util_change(cfs_rq);
}

static inline void remove_entity_load_avg(struct sched_entity *se) {}
--
2.17.1