linux-kernel - Re: [PATCH V4 1/3] sched: cpufreq: Allow remote cpufreq callbacks

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Date:   Wed, 26 Jul 2017 19:42:01 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        smuckle.linux@...il.com, juri.lelli@....com,
        Morten.Rasmussen@....com, patrick.bellasi@....com,
        eas-dev@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 1/3] sched: cpufreq: Allow remote cpufreq callbacks

On Wednesday, July 26, 2017 02:52:32 PM Viresh Kumar wrote:
> We do not call cpufreq callbacks from scheduler core for remote
> (non-local) CPUs currently. But there are cases where such remote
> callbacks are useful, specially in the case of shared cpufreq policies.
> 
> This patch updates the scheduler core to call the cpufreq callbacks for
> remote CPUs as well.
> 
> For now, all the registered utilization update callbacks are updated to
> return early if remote callback is detected. That is, this patch just
> moves the decision making down in the hierarchy.
> 
> Later patches would enable remote callbacks for shared policies.
> 
> Based on initial work from Steve Muckle.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/cpufreq/cpufreq_governor.c |  4 ++++
>  drivers/cpufreq/intel_pstate.c     |  8 ++++++++
>  include/linux/sched/cpufreq.h      |  1 +
>  kernel/sched/cpufreq.c             |  1 +
>  kernel/sched/cpufreq_schedutil.c   | 11 ++++++++---
>  kernel/sched/deadline.c            |  2 +-
>  kernel/sched/fair.c                |  8 +++++---
>  kernel/sched/rt.c                  |  2 +-
>  kernel/sched/sched.h               | 10 ++--------
>  9 files changed, 31 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
> index eed069ecfd5e..5499796cf9a8 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -272,6 +272,10 @@ static void dbs_update_util_handler(struct update_util_data *data, u64 time,
>  	struct policy_dbs_info *policy_dbs = cdbs->policy_dbs;
>  	u64 delta_ns, lst;
>  
> +	/* Don't allow remote callbacks */
> +	if (smp_processor_id() != data->cpu)
> +		return;
> +
>  	/*
>  	 * The work may not be allowed to be queued up right now.
>  	 * Possible reasons:
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 89bbc0c11b22..0dd14c8edd2d 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -1747,6 +1747,10 @@ static void intel_pstate_update_util_pid(struct update_util_data *data,
>  	struct cpudata *cpu = container_of(data, struct cpudata, update_util);
>  	u64 delta_ns = time - cpu->sample.time;
>  
> +	/* Don't allow remote callbacks */
> +	if (smp_processor_id() != data->cpu)
> +		return;

You can do this check against cpu->cpu, however.

> +
>  	if ((s64)delta_ns < pid_params.sample_rate_ns)
>  		return;
>  
> @@ -1764,6 +1768,10 @@ static void intel_pstate_update_util(struct update_util_data *data, u64 time,
>  	struct cpudata *cpu = container_of(data, struct cpudata, update_util);
>  	u64 delta_ns;
>  
> +	/* Don't allow remote callbacks */
> +	if (smp_processor_id() != data->cpu)
> +		return;

And same here.

> +
>  	if (flags & SCHED_CPUFREQ_IOWAIT) {
>  		cpu->iowait_boost = int_tofp(1);
>  	} else if (cpu->iowait_boost) {
> diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
> index d2be2ccbb372..8256a8f35f22 100644
> --- a/include/linux/sched/cpufreq.h
> +++ b/include/linux/sched/cpufreq.h
> @@ -16,6 +16,7 @@
>  #ifdef CONFIG_CPU_FREQ
>  struct update_util_data {
>         void (*func)(struct update_util_data *data, u64 time, unsigned int flags);
> +       unsigned int cpu;

So it looks like you don't need this.

schedutil doesn't need it as per patch [2/3].

ondemand/conservative don't need it as per patch [3/3]

intel_pstate doesn't need this too, because of the above.

Thanks,
Rafael