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

[Peter Zijlstra]

On Wed, Jan 15, 2020 at 11:20:20AM +0100, 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>

Thanks!