linux-kernel - Re: [RFC/RFT] [PATCH 07/10] cpufreq: intel_pstate: HWP boost performance on busy task migrate

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Date:   Wed, 16 May 2018 11:49:38 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>, Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Mel Gorman <mgorman@...hsingularity.net>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Juri Lelli <juri.lelli@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/RFT] [PATCH 07/10] cpufreq: intel_pstate: HWP boost
 performance on busy task migrate

On Wed, May 16, 2018 at 6:49 AM, Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
> When a busy task migrates to a new CPU boost HWP prformance to max. This
> helps workloads on servers with per core P-states, which saturates all
> CPUs and then they migrate frequently. But changing limits has extra over
> head of issuing new HWP Request MSR, which takes 1000+
> cycles. So this change limits setting HWP Request MSR.
> Rate control in setting HWP Requests:
> - If the current performance is around P1, simply ignore.
> - Once set wait till hold time, till remove boost. While the boost
>  is on, another flags is notified, it will prolong boost.
> - The task migrates needs to have some utilzation which is more
> than threshold utilization, which will trigger P-state above minimum.
>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> ---
>  drivers/cpufreq/intel_pstate.c | 37 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 36 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index d418265..ec455af 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -227,6 +227,7 @@ struct global_params {
>   *                     defines callback and arguments
>   * @hwp_boost_active:  HWP performance is boosted on this CPU
>   * @last_io_update:    Last time when IO wake flag was set
> + * @migrate_hint:      Set when scheduler indicates thread migration
>   *
>   * This structure stores per CPU instance data for all CPUs.
>   */
> @@ -263,6 +264,7 @@ struct cpudata {
>         call_single_data_t csd;
>         bool hwp_boost_active;
>         u64 last_io_update;
> +       bool migrate_hint;

Why do you need this in the struct?

It looks like it only is used locally in intel_pstate_update_util_hwp().

>  };