Re: [PATCH 1/5] cpufreq: amd-pstate: cpufreq: amd-pstate: reset MSR_AMD_PERF_CTL register at init

[Gautham R. Shenoy]

On Thu, Nov 17, 2022 at 10:49:51AM +0800, Perry Yuan wrote:
> From: Wyes Karny <wyes.karny@xxxxxxx>
> 
> MSR_AMD_PERF_CTL is guaranteed to be 0 on a cold boot. However, on a
> kexec boot, for instance, it may have a non-zero value (if the cpu was
> in a non-P0 Pstate).  In such cases, the cores with non-P0 Pstates at
> boot will never be pushed to P0, let alone boost frequencies.
> 
> Kexec is a common workflow for reboot on Linux and this creates a
> regression in performance. Fix it by explicitly setting the
> MSR_AMD_PERF_CTL to 0 during amd_pstate driver init.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Wyes Karny <wyes.karny@xxxxxxx>
> Signed-off-by: Perry Yuan <Perry.Yuan@xxxxxxx>

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@xxxxxxx>

> ---
>  drivers/cpufreq/amd-pstate.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index ace7d50cf2ac..d844c6f97caf 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -424,12 +424,22 @@ static void amd_pstate_boost_init(struct amd_cpudata *cpudata)
>  	amd_pstate_driver.boost_enabled = true;
>  }
>  
> +static void amd_perf_ctl_reset(unsigned int cpu)
> +{
> +	wrmsrl_on_cpu(cpu, MSR_AMD_PERF_CTL, 0);
> +}
> +
>  static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>  {
>  	int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
>  	struct device *dev;
>  	struct amd_cpudata *cpudata;
>  
> +	/*
> +	 * Resetting PERF_CTL_MSR will put the CPU in P0 frequency,
> +	 * which is ideal for initialization process.
> +	 */
> +	amd_perf_ctl_reset(policy->cpu);
>  	dev = get_cpu_device(policy->cpu);
>  	if (!dev)
>  		return -ENODEV;
> -- 
> 2.25.1
>