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

Wyes Karny
2022-11-17T05:04:06Z

On 11/17/2022 8:19 AM, Perry Yuan wrote:
> From: Wyes Karny <wyes.karny@amd.com>
>
> 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@vger.kernel.org
> Signed-off-by: Wyes Karny <wyes.karny@amd.com>
> Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>

Tested-by: Wyes Karny <wyes.karny@amd.com>

> ---
> 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;

--
Thanks & Regards,
Wyes