Re: [PATCH v3 3/6] cpufreq: schedutil: update CFS util only if used

[Juri Lelli]

Hi,

On 30/11/17 11:47, Patrick Bellasi wrote:
> Currently the utilization of the FAIR class is collected before locking
> the policy. Although that should not be a big issue for most cases, we
> also don't really know how much latency there can be between the
> utilization reading and its usage.
> 
> Let's get the FAIR utilization right before its usage to be better in
> sync with the current status of a CPU.
> 
> Signed-off-by: Patrick Bellasi <patrick.bellasi@xxxxxxx>
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-pm@xxxxxxxxxxxxxxx
> 
> ---
> Changes from v2:
> - rebased on v4.15-rc1
> 
> Change-Id: I9291a560bcad7db76894e3f0fcdb917511d0479e
> ---
>  kernel/sched/cpufreq_schedutil.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 448f49de5335..40521d59630b 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -351,10 +351,9 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
>  	unsigned int next_f;
>  	bool rt_mode;
>  
> -	sugov_get_util(&util, &max, sg_cpu->cpu);
> -
>  	raw_spin_lock(&sg_policy->update_lock);
>  
> +	sugov_get_util(&util, &max, sg_cpu->cpu);
>  	sg_cpu->util = util;
>  	sg_cpu->max = max;

Patch looks good.

Reviewed-by: Juri Lelli <juri.lelli@xxxxxxxxxx>

However, not sure $SUBJECT is really in sync with what the patch does?
CFS gets "used" before and after the patch... last paragraph of the
changelog looks more like it. :)

Best,

Juri