linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Use HWP capabilities in intel_cpufreq_adjust

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Date:   Tue, 05 Jan 2021 22:59:43 -0800
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: intel_pstate: Use HWP capabilities in
 intel_cpufreq_adjust_perf()

On Tue, 2021-01-05 at 19:20 +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> If turbo P-states cannot be used, either due to the configuration of
> the processor, or because intel_pstate is not allowed to used them,
> the maximum available P-state with HWP enabled corresponds to the
> HWP_CAP.GUARANTEED value which is not static.  It can be adjusted by
> an out-of-band agent or during an Intel Speed Select performance
> level change, so long as it remains less than or equal to
> HWP_CAP.MAX.
> 
> However, if turbo P-states cannot be used,
> intel_cpufreq_adjust_perf()
> always uses pstate.max_pstate (set during the initialization of the
> driver only) as the maximum available P-state, so it may miss a
> change
> of the HWP_CAP.GUARANTEED value.
> 
> Prevent that from happening by modifyig intel_cpufreq_adjust_perf()
> to always read the "guaranteed" and "maximum turbo" performance
> levels from the cached HWP_CAP value.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>

> ---
>  drivers/cpufreq/intel_pstate.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -2653,12 +2653,13 @@ static void intel_cpufreq_adjust_perf(un
>                                       unsigned long capacity)
>  {
>         struct cpudata *cpu = all_cpu_data[cpunum];
> +       u64 hwp_cap = READ_ONCE(cpu->hwp_cap_cached);
>         int old_pstate = cpu->pstate.current_pstate;
>         int cap_pstate, min_pstate, max_pstate, target_pstate;
>  
>         update_turbo_state();
> -       cap_pstate = global.turbo_disabled ? cpu->pstate.max_pstate :
> -                                            cpu-
> >pstate.turbo_pstate;
> +       cap_pstate = global.turbo_disabled ?
> HWP_GUARANTEED_PERF(hwp_cap) :
> +                                           
> HWP_HIGHEST_PERF(hwp_cap);
>  
>         /* Optimization: Avoid unnecessary divisions. */
>  
> 
> 
>