Date: Thu, 14 Mar 2024 15:11:36 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Perry Yuan <perry.yuan@....com>
Cc: rafael.j.wysocki@...el.com, Mario.Limonciello@....com,
	viresh.kumar@...aro.org, Ray.Huang@....com, Borislav.Petkov@....com,
	Alexander.Deucher@....com, Xinmei.Huang@....com,
	Xiaojian.Du@....com, Li.Meng@....com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/7] cpufreq: amd-pstate: implement cpb_boost sysfs
 entry for boost control

Hello Perry,


On Wed, Mar 13, 2024 at 06:04:39PM +0800, Perry Yuan wrote:
> From: Perry Yuan <Perry.Yuan@....com>
> 
> With this new sysfs entry `cpb_boost`created, user can change CPU boost
> state dynamically under `active`, `guided` and `passive` modes.
> And the highest perf and frequency will also be updated as the boost
> state changing.
> 
> 0): check current boost state
> cat /sys/devices/system/cpu/amd_pstate/cpb_boost

Could you please elaborate on the need for this new interface when
/sys/devices/system/cpu/cpufreq/boost exists and is being used in the
other cpufreq driver namely the acpi-cpufreq driver ?

The semantics of this new interface seems to be identical to the
existing boost interface.

I am ok with the rest of the patch, but please explain the need for a
new interface.

--
Thanks and Regards
gautham.

> 
> 1): disable CPU boost
> sudo bash -c "echo 0 > /sys/devices/system/cpu/amd_pstate/cpb_boost"
> 
> 2): enable CPU boost
> sudo bash -c "echo 1 > /sys/devices/system/cpu/amd_pstate/cpb_boost"
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217931
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217618
> Signed-off-by: Perry Yuan <Perry.Yuan@....com>
> ---
>  drivers/cpufreq/amd-pstate.c | 97 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 97 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index ef6381b48e76..d54399ebb758 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1208,6 +1208,101 @@ static ssize_t prefcore_show(struct device *dev,
>  	return sysfs_emit(buf, "%s\n", str_enabled_disabled(amd_pstate_prefcore));
>  }
>  
> +static int amd_cpu_boost_update(struct amd_cpudata *cpudata, u32 on)
> +{
> +	struct cpufreq_policy *policy = cpufreq_cpu_acquire(cpudata->cpu);
> +	struct cppc_perf_ctrls perf_ctrls;
> +	u32 highest_perf, nominal_perf;
> +	int ret;
> +
> +	if (!policy)
> +		return -ENODATA;
> +
> +	highest_perf = READ_ONCE(cpudata->highest_perf);
> +	nominal_perf = READ_ONCE(cpudata->nominal_perf);
> +
> +	if (boot_cpu_has(X86_FEATURE_CPPC)) {
> +		u64 value = READ_ONCE(cpudata->cppc_req_cached);
> +
> +		value &= ~GENMASK_ULL(7, 0);
> +		value |= on ? highest_perf : nominal_perf;
> +		WRITE_ONCE(cpudata->cppc_req_cached, value);
> +
> +		wrmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ, value);
> +
> +	} else {
> +		perf_ctrls.max_perf = on ? highest_perf : nominal_perf;
> +		ret = cppc_set_epp_perf(cpudata->cpu, &perf_ctrls, 1);
> +		if (ret) {
> +			pr_debug("failed to set energy perf value (%d)\n", ret);
> +			return ret;
> +		}
> +	}
> +
> +	if (on)
> +		policy->cpuinfo.max_freq = cpudata->max_freq;
> +	else
> +		policy->cpuinfo.max_freq = cpudata->nominal_freq * 1000;
> +
> +	policy->max = policy->cpuinfo.max_freq;
> +
> +	if (cppc_state == AMD_PSTATE_PASSIVE) {
> +		ret = freq_qos_update_request(&cpudata->req[1],
> +				      policy->cpuinfo.max_freq);
> +	}
> +
> +	cpufreq_cpu_release(policy);
> +
> +	return ret;
> +}
> +
> +static ssize_t cpb_boost_show(struct device *dev,
> +			   struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%u\n", amd_pstate_global_params.cpb_boost);
> +}
> +
> +static ssize_t cpb_boost_store(struct device *dev, struct device_attribute *b,
> +			    const char *buf, size_t count)
> +{
> +	bool new_state;
> +	ssize_t ret;
> +	int cpu;
> +
> +	mutex_lock(&amd_pstate_driver_lock);
> +	if (!amd_pstate_global_params.cpb_supported) {
> +		pr_err("Boost mode is not supported by this processor or SBIOS\n");
> +		return -EINVAL;
> +	}
> +
> +	ret = kstrtobool(buf, &new_state);
> +	if (ret)
> +		return -EINVAL;
> +
> +	amd_pstate_global_params.cpb_boost = !!new_state;
> +
> +	for_each_online_cpu(cpu) {
> +
> +		struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
> +		struct amd_cpudata *cpudata = policy->driver_data;
> +
> +		if (!cpudata) {
> +			pr_err("cpudata is NULL\n");
> +			ret = -ENODATA;
> +			cpufreq_cpu_put(policy);
> +			goto err_exit;
> +		}
> +
> +		amd_cpu_boost_update(cpudata, amd_pstate_global_params.cpb_boost);
> +		refresh_frequency_limits(policy);
> +		cpufreq_cpu_put(policy);
> +	}
> +
> +err_exit:
> +	mutex_unlock(&amd_pstate_driver_lock);
> +	return ret < 0 ? ret : count;
> +}
> +
>  cpufreq_freq_attr_ro(amd_pstate_max_freq);
>  cpufreq_freq_attr_ro(amd_pstate_lowest_nonlinear_freq);
>  
> @@ -1218,6 +1313,7 @@ cpufreq_freq_attr_rw(energy_performance_preference);
>  cpufreq_freq_attr_ro(energy_performance_available_preferences);
>  static DEVICE_ATTR_RW(status);
>  static DEVICE_ATTR_RO(prefcore);
> +static DEVICE_ATTR_RW(cpb_boost);
>  
>  static struct freq_attr *amd_pstate_attr[] = {
>  	&amd_pstate_max_freq,
> @@ -1242,6 +1338,7 @@ static struct freq_attr *amd_pstate_epp_attr[] = {
>  static struct attribute *pstate_global_attributes[] = {
>  	&dev_attr_status.attr,
>  	&dev_attr_prefcore.attr,
> +	&dev_attr_cpb_boost.attr,
>  	NULL
>  };
>  
> -- 
> 2.34.1
> 

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