linux-kernel - Re: [PATCH V2 3/4] intel_pstate: Ignore scheduler cpufreq callbacks on remote CPUs

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Message-ID: <1498771438.7952.118.camel@linux.intel.com>
Date:   Thu, 29 Jun 2017 14:23:58 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Len Brown <lenb@...nel.org>
Cc:     linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org, smuckle.linux@...il.com,
        juri.lelli@....com, Morten.Rasmussen@....com,
        patrick.bellasi@....com, eas-dev@...ts.linaro.org
Subject: Re: [PATCH V2 3/4] intel_pstate: Ignore scheduler cpufreq callbacks
 on remote CPUs

On Thu, 2017-06-29 at 10:56 +0530, Viresh Kumar wrote:
> From: Steve Muckle <smuckle.linux@...il.com>
> 
> In preparation for the scheduler cpufreq callback happening on remote
> CPUs, check for this case in intel_pstate which currently requires
> the
> callback run on the local CPU. Such callbacks are ignored for now.
Is it possible that we miss a chance to calculate load periodically at
a predefined interval (10ms default), because the callback happened on
a different CPU?

Thanks,
Srinivas

> 
> Signed-off-by: Steve Muckle <smuckle.linux@...il.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/cpufreq/intel_pstate.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c
> b/drivers/cpufreq/intel_pstate.c
> index 4ce501148790..7a2a8ee579ef 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -1755,6 +1755,9 @@ 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;
>  
> +	if (smp_processor_id() != data->cpu)
> +		return;
> +
>  	if (flags & SCHED_CPUFREQ_IOWAIT) {
>  		cpu->iowait_boost = int_tofp(1);
>  	} else if (cpu->iowait_boost) {