linux-kernel - Re: [PATCH] Revert "cpufreq: intel_pstate: Fix ->set_policy() interface for no

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Date:   Sat, 4 Aug 2018 19:31:50 +0200
From:   Gabriele Mazzotta <gabriele.mzt@...il.com>
To:     srinivas.pandruvada@...ux.intel.com, rjw@...ysocki.net
Cc:     lenb@...nel.org, viresh.kumar@...aro.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "cpufreq: intel_pstate: Fix ->set_policy()
 interface for no_turbo"

On 04/08/2018 17:29, Gabriele Mazzotta wrote:
> This change does not take into account that some BIOSes change
> MSR_IA32_MISC_ENABLE_TURBO_DISABLE depending on the power source.
> If the turbo is disabled when the system boots, policy.max_freq
> is set to pstate.max_pstate. However, if the BIOS later enables
> the turbo, the CPU will never be able to run at pstate.turbo_pstate.
> 
> Since now intel_pstate_set_policy() does its calculations using
> pstate.max_freq and pstate.turbo_freq, we can always calculate
> cpuinfo.max_freq using pstate.turbo_pstate, thus allowing system
> with varying MSR_IA32_MISC_ENABLE_TURBO_DISABLE to run at full
> speed when the turbo is enabled.
> 
> This reverts commit 983e600e88835f0321d1a0ea06f52d48b7b5a544.
> 
> Signed-off-by: Gabriele Mazzotta <gabriele.mzt@...il.com>
> ---
>  drivers/cpufreq/intel_pstate.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 3c3971256130..4043aae2d611 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -2068,9 +2068,8 @@ static int __intel_pstate_cpu_init(struct cpufreq_policy *policy)
>  	/* cpuinfo and default policy values */
>  	policy->cpuinfo.min_freq = cpu->pstate.min_pstate * cpu->pstate.scaling;
>  	update_turbo_state();

Commit 983e600e8883 added this update_turbo_state() call, but it is
needed by intel_pstate_init_acpi_perf_limits() here below. I should
have mentioned it in the commit message.

However, I've just realized that a similar problem to that I'm trying
to fix can occur on those systems where core_frequency is adjusted
depending on the availability of the turbo.

The call to update_turbo_state() could also be moved in
intel_pstate_init_acpi_perf_limits(), right before the check on
global.turbo_disabled.

> -	policy->cpuinfo.max_freq = global.turbo_disabled ?
> -			cpu->pstate.max_pstate : cpu->pstate.turbo_pstate;
> -	policy->cpuinfo.max_freq *= cpu->pstate.scaling;
> +	policy->cpuinfo.max_freq =
> +		cpu->pstate.turbo_pstate * cpu->pstate.scaling;
>  
>  	intel_pstate_init_acpi_perf_limits(policy);
>  
>