linux-kernel - Re: [PATCH v2 02/14] cpufreq: amd-pstate: enable AMD Precision Boost mode switch

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Date:   Mon, 11 Jul 2022 14:26:48 -0500
From:   Nathan Fontenot <nafonten@....com>
To:     Perry Yuan <Perry.Yuan@....com>, rafael.j.wysocki@...el.com,
        viresh.kumar@...aro.org, Ray.Huang@....com
Cc:     Deepak.Sharma@....com, Mario.Limonciello@....com,
        Nathan.Fontenot@....com, Alexander.Deucher@....com,
        Jinzhou.Su@....com, Xinmei.Huang@....com, Xiaojian.Du@....com,
        Li.Meng@....com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/14] cpufreq: amd-pstate: enable AMD Precision Boost
 mode switch

On 7/9/22 09:17, Perry Yuan wrote:
> Add support to switch AMD precision boost state to scale cpu max
> frequency that will help to improve the processor throughput.
> 
> when set boost state to be enabled, user will need to execute below commands,
> the CPU will reach absolute maximum performance level or the highest perf which
> CPU physical support. This performance level may not be sustainable for
> long durations, it will help to improve the IO workload tasks.
> 
> * turn on CPU boost state under root
>   echo 1 > /sys/devices/system/cpu/cpufreq/boost
> 
> If user set boost off,the CPU can reach to the maximum sustained
> performance level of the process, that level is the process can maintain
> continously working and definitely it can save some power compared to
> boost on mode.
> 
> * turn off CPU boost state under root
>   echo 0 > /sys/devices/system/cpu/cpufreq/boost
> 
> Signed-off-by: Perry Yuan <Perry.Yuan@....com>
> ---
>  arch/x86/include/asm/msr-index.h |  2 ++
>  drivers/cpufreq/amd-pstate.c     | 22 +++++++++++++++++++---
>  2 files changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 869508de8269..b952fd6d6916 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -559,6 +559,8 @@
>  #define AMD_CPPC_MIN_PERF(x)		(((x) & 0xff) << 8)
>  #define AMD_CPPC_DES_PERF(x)		(((x) & 0xff) << 16)
>  #define AMD_CPPC_ENERGY_PERF_PREF(x)	(((x) & 0xff) << 24)
> +#define AMD_CPPC_PRECISION_BOOST_BIT	25
> +#define AMD_CPPC_PRECISION_BOOST_ENABLED	BIT_ULL(AMD_CPPC_PRECISION_BOOST_BIT)
>  
>  /* AMD Performance Counter Global Status and Control MSRs */
>  #define MSR_AMD64_PERF_CNTR_GLOBAL_STATUS	0xc0000300
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 9ac75c1cde9c..188e055e24a2 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -122,6 +122,7 @@ struct amd_cpudata {
>  
>  	u64 freq;
>  	bool	boost_supported;
> +	u64 	cppc_hw_conf_cached;
>  };
>  
>  static inline int pstate_enable(bool enable)
> @@ -438,18 +439,27 @@ static int amd_pstate_set_boost(struct cpufreq_policy *policy, int state)
>  {
>  	struct amd_cpudata *cpudata = policy->driver_data;
>  	int ret;
> +	u64 value;
>  
>  	if (!cpudata->boost_supported) {
>  		pr_err("Boost mode is not supported by this processor or SBIOS\n");
>  		return -EINVAL;
>  	}
>  
> -	if (state)
> +	ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_HW_CTL, &value);
> +	if (ret)
> +		return ret;
> +
> +	if (state) {
> +		value |= AMD_CPPC_PRECISION_BOOST_ENABLED;
>  		policy->cpuinfo.max_freq = cpudata->max_freq;
> -	else
> +	} else {
> +		value &= ~AMD_CPPC_PRECISION_BOOST_ENABLED;
>  		policy->cpuinfo.max_freq = cpudata->nominal_freq;
> -
> +	}
>  	policy->max = policy->cpuinfo.max_freq;
> +	WRITE_ONCE(cpudata->cppc_hw_conf_cached, value);

Does the entire MSR value need to be cached? We only care about the boost enabled
bit so it may be better to just cache that.

-Nathan

> +	wrmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_HW_CTL, value);
>  
>  	ret = freq_qos_update_request(&cpudata->req[1],
>  				      policy->cpuinfo.max_freq);
> @@ -478,6 +488,7 @@ 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;
> +	u64 value;
>  
>  	dev = get_cpu_device(policy->cpu);
>  	if (!dev)
> @@ -542,6 +553,11 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>  
>  	policy->driver_data = cpudata;
>  
> +	ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_HW_CTL, &value);
> +	if (ret)
> +		return ret;
> +	WRITE_ONCE(cpudata->cppc_hw_conf_cached, value);
> +
>  	amd_pstate_boost_init(cpudata);
>  
>  	return 0;