linux-kernel - Re: [PATCH v2] cpufreq/amd-pstate: Write CPPC enable bit per-socket

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Date:   Fri, 16 Jun 2023 15:03:09 +0800
From:   Huang Rui <ray.huang@....com>
To:     "Karny, Wyes" <Wyes.Karny@....com>
Cc:     "rafael@...nel.org" <rafael@...nel.org>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        "Yuan, Perry" <Perry.Yuan@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Shenoy, Gautham Ranjal" <gautham.shenoy@....com>
Subject: Re: [PATCH v2] cpufreq/amd-pstate: Write CPPC enable bit per-socket

On Tue, May 30, 2023 at 09:13:48PM +0800, Karny, Wyes wrote:
> Currently amd_pstate sets CPPC enable bit in MSR_AMD_CPPC_ENABLE only
> for the CPU where the module_init happened. But MSR_AMD_CPPC_ENABLE is
> per-socket. This causes CPPC enable bit to set for only one socket for
> servers with more than one physical packages. To fix this write
> MSR_AMD_CPPC_ENABLE per-socket.
> 
> Also, handle duplicate calls for cppc_enable, because it's called from
> per-policy/per-core callbacks and can result in duplicate MSR writes.
> 
> Before the fix:
> amd@amd:~$ sudo rdmsr -a 0xc00102b1 | uniq --count
> 	192 0
>     192 1
> 
> After the fix:
> amd@amd:~$ sudo rdmsr -a 0xc00102b1 | uniq --count
>     384 1
> 
> Suggested-by: Gautham R. Shenoy <gautham.shenoy@....com>
> Signed-off-by: Wyes Karny <wyes.karny@....com>
> ---
> v1 -> v2:
> - Made CPPC enable read/write per-socket
> 
>  drivers/cpufreq/amd-pstate.c | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 5a3d4aa0f45a..45b9e359f638 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -63,6 +63,7 @@ static struct cpufreq_driver *current_pstate_driver;
>  static struct cpufreq_driver amd_pstate_driver;
>  static struct cpufreq_driver amd_pstate_epp_driver;
>  static int cppc_state = AMD_PSTATE_DISABLE;
> +static bool cppc_enabled;
>  
>  /*
>   * AMD Energy Preference Performance (EPP)
> @@ -228,7 +229,28 @@ static int amd_pstate_set_energy_pref_index(struct amd_cpudata *cpudata,
>  
>  static inline int pstate_enable(bool enable)
>  {
> -	return wrmsrl_safe(MSR_AMD_CPPC_ENABLE, enable);
> +	int ret, cpu;
> +	unsigned long logical_proc_id_mask = 0;
> +
> +	if (enable == cppc_enabled)
> +		return 0;
> +
> +	for_each_present_cpu(cpu) {
> +		unsigned long logical_id = topology_logical_die_id(cpu);
> +
> +		if (test_bit(logical_id, &logical_proc_id_mask))
> +			continue;
> +
> +		set_bit(logical_id, &logical_proc_id_mask);
> +
> +		ret = wrmsrl_safe_on_cpu(cpu, MSR_AMD_CPPC_ENABLE,
> +				enable);

Thanks Wyes, that makes a lot more sense to me. The MSR is per package on
design. We should only write once per package.

Patch is

Acked-by: Huang Rui <ray.huang@....com>

> +		if (ret)
> +			return ret;
> +	}
> +
> +	cppc_enabled = enable;
> +	return 0;
>  }
>  
>  static int cppc_enable(bool enable)
> @@ -236,6 +258,9 @@ static int cppc_enable(bool enable)
>  	int cpu, ret = 0;
>  	struct cppc_perf_ctrls perf_ctrls;
>  
> +	if (enable == cppc_enabled)
> +		return 0;
> +
>  	for_each_present_cpu(cpu) {
>  		ret = cppc_set_enable(cpu, enable);
>  		if (ret)
> @@ -251,6 +276,7 @@ static int cppc_enable(bool enable)
>  		}
>  	}
>  
> +	cppc_enabled = enable;
>  	return ret;
>  }
>  
> -- 
> 2.34.1
>