linux-kernel - Re: [PATCH v4 1/5] cpufreq/amd-pstate: Add dynamic energy performance preference

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Message-ID: <4d224956-b4f9-4b0c-b5fb-70abe82e6ab5@amd.com>
Date: Mon, 24 Mar 2025 15:28:51 +0530
From: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>
To: Mario Limonciello <superm1@...nel.org>,
 "Gautham R . Shenoy" <gautham.shenoy@....com>,
 Perry Yuan <perry.yuan@....com>
Cc: "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
 <linux-kernel@...r.kernel.org>,
 "open list:CPU FREQUENCY SCALING FRAMEWORK" <linux-pm@...r.kernel.org>,
 Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v4 1/5] cpufreq/amd-pstate: Add dynamic energy performance
 preference

On 3/21/2025 7:58 AM, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@....com>
> 
> Dynamic energy performance preference will change the EPP profile
> based on whether the machine is running on AC or DC power.
> 
> A notification chain from the power supply core is used to adjust
> EPP values on plug in or plug out events.
> 
> For non-server systems:
>     * the default EPP for AC mode is `performance`.
>     * the default EPP for DC mode is `balance_performance`.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
> v3->v4:
>  * Handle Kconfig not being set
>  * Fix dynamic epp default on server
> v2-v3:
>  * Fix typo in Kconfig
> v1->v2:
>  * Change defaults to performance (AC) and balance_performance (DC)
>  * Default Kconfig to disabled for now
>  * Rebase on latest branch
> ---
>  Documentation/admin-guide/pm/amd-pstate.rst |  18 ++-
>  drivers/cpufreq/Kconfig.x86                 |  12 ++
>  drivers/cpufreq/amd-pstate.c                | 135 +++++++++++++++++++-
>  drivers/cpufreq/amd-pstate.h                |   5 +-
>  4 files changed, 161 insertions(+), 9 deletions(-)
> 
[snip]
> @@ -1050,6 +1056,73 @@ static void amd_pstate_cpu_exit(struct cpufreq_policy *policy)
>  	kfree(cpudata);
>  }
>  
> +static int amd_pstate_get_balanced_epp(struct cpufreq_policy *policy)
> +{
> +	struct amd_cpudata *cpudata = policy->driver_data;
> +
> +	if (power_supply_is_system_supplied())
> +		return cpudata->epp_default_ac;
> +	else
> +		return cpudata->epp_default_dc;
> +}
> +
> +static int amd_pstate_power_supply_notifier(struct notifier_block *nb,
> +					    unsigned long event, void *data)
> +{
> +	struct amd_cpudata *cpudata = container_of(nb, struct amd_cpudata, power_nb);
> +	struct cpufreq_policy *policy __free(put_cpufreq_policy) = cpufreq_cpu_get(cpudata->cpu);

For consistency, we should add "if (!policy)" check I think

> +	u8 epp;
> +	int ret;
> +
> +	if (event != PSY_EVENT_PROP_CHANGED)
> +		return NOTIFY_OK;
> +
> +	epp = amd_pstate_get_balanced_epp(policy);
> +
> +	ret = amd_pstate_set_epp(policy, epp);
> +	if (ret)
> +		pr_warn("Failed to set CPU %d EPP %u: %d\n", cpudata->cpu, epp, ret);
> +
> +	return NOTIFY_OK;
> +}
[snip]
> @@ -1364,6 +1444,32 @@ static ssize_t prefcore_show(struct device *dev,
>  	return sysfs_emit(buf, "%s\n", str_enabled_disabled(amd_pstate_prefcore));
>  }
>  
> +static ssize_t dynamic_epp_show(struct device *dev,
> +				struct device_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%s\n", str_enabled_disabled(dynamic_epp));
> +}
> +
> +static ssize_t dynamic_epp_store(struct device *a, struct device_attribute *b,
> +				 const char *buf, size_t count)
> +{
> +	bool enabled;
> +	int ret;
> +
> +	ret = kstrtobool(buf, &enabled);
> +	if (ret)
> +		return ret;
> +
> +	if (dynamic_epp == enabled)
> +		return -EINVAL;
> +
> +	/* reinitialize with desired dynamic EPP value */
> +	dynamic_epp = enabled;
> +	ret = amd_pstate_change_driver_mode(cppc_state);

I think implicitly changing the driver mode when we write to dynamic_epp file might lead to some confusions.

> +
> +	return ret ? ret : count;
> +}
> +
>  cpufreq_freq_attr_ro(amd_pstate_max_freq);
>  cpufreq_freq_attr_ro(amd_pstate_lowest_nonlinear_freq);