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Message-ID: <301ad0d4-f8be-4787-ba3d-e4311e5c386f@amd.com>
Date: Mon, 24 Mar 2025 16:14:11 +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 4/5] cpufreq/amd-pstate: Add support for raw EPP writes
On 3/21/2025 7:58 AM, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@....com>
>
> The energy performance preference field of the CPPC request MSR
> supports values from 0 to 255, but the strings only offer 4 values.
>
> The other values are useful for tuning the performance of some
> workloads.
>
> Add support for writing the raw energy performance preference value
> to the sysfs file. If the last value written was an integer then
> an integer will be returned. If the last value written was a string
> then a string will be returned.
LGTM
Reviewed-by: Dhananjay Ugwekar <dhananjay.ugwekar@....com>
>
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
> Documentation/admin-guide/pm/amd-pstate.rst | 16 +++++++++++-----
> drivers/cpufreq/amd-pstate.c | 11 +++++++++--
> drivers/cpufreq/amd-pstate.h | 1 +
> 3 files changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
> index 36950fb6568c0..0e4d2e0aaeff7 100644
> --- a/Documentation/admin-guide/pm/amd-pstate.rst
> +++ b/Documentation/admin-guide/pm/amd-pstate.rst
> @@ -280,16 +280,22 @@ A list of all the supported EPP preferences that could be used for
> These profiles represent different hints that are provided
> to the low-level firmware about the user's desired energy vs efficiency
> tradeoff. ``default`` represents the epp value is set by platform
> -firmware. This attribute is read-only.
> +firmware. ``custom`` designates that integer values 0-255 may be written
> +as well. This attribute is read-only.
>
> ``energy_performance_preference``
>
> The current energy performance preference can be read from this attribute.
> and user can change current preference according to energy or performance needs
> -Please get all support profiles list from
> -``energy_performance_available_preferences`` attribute, all the profiles are
> -integer values defined between 0 to 255 when EPP feature is enabled by platform
> -firmware, but if the dynamic EPP feature is enabled, driver will block writes.
> +Coarse named profiles are available in the attribute
> +``energy_performance_available_preferences``.
> +Users can also write individual integer values between 0 to 255.
> +When EPP feature is enabled by platform firmware but if the dynamic EPP feature is
> +enabled, driver will ignore the written value. Lower epp values shift the bias
> +towards improved performance while a higher epp value shifts the bias towards
> +power-savings. The exact impact can change from one platform to the other.
> +If a valid integer was last written, then a number will be returned on future reads.
> +If a valid string was last written then a string will be returned on future reads.
> This attribute is read-write.
>
> ``boost``
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 2a62b12148544..b0de50f390e07 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1318,6 +1318,7 @@ ssize_t store_energy_performance_preference(struct cpufreq_policy *policy,
> struct amd_cpudata *cpudata = policy->driver_data;
> char str_preference[21];
> ssize_t ret;
> + bool raw_epp = FALSE;
> u8 epp;
>
> if (cpudata->dynamic_epp) {
> @@ -1334,6 +1335,7 @@ ssize_t store_energy_performance_preference(struct cpufreq_policy *policy,
> * matches an index in the energy_perf_strings array
> */
> ret = kstrtou8(str_preference, 0, &epp);
> + raw_epp = !ret;
> if (ret) {
> ret = match_string(energy_perf_strings, -1, str_preference);
> if (ret < 0 || ret == EPP_INDEX_CUSTOM)
> @@ -1353,7 +1355,9 @@ ssize_t store_energy_performance_preference(struct cpufreq_policy *policy,
> if (ret)
> return ret;
>
> - return ret ? ret : count;
> + cpudata->raw_epp = raw_epp;
> +
> + return count;
> }
> EXPORT_SYMBOL_GPL(store_energy_performance_preference);
>
> @@ -1364,6 +1368,9 @@ ssize_t show_energy_performance_preference(struct cpufreq_policy *policy, char *
>
> epp = FIELD_GET(AMD_CPPC_EPP_PERF_MASK, cpudata->cppc_req_cached);
>
> + if (cpudata->raw_epp)
> + return sysfs_emit(buf, "%u\n", epp);
> +
> switch (epp) {
> case AMD_CPPC_EPP_PERFORMANCE:
> preference = EPP_INDEX_PERFORMANCE;
> @@ -1378,7 +1385,7 @@ ssize_t show_energy_performance_preference(struct cpufreq_policy *policy, char *
> preference = EPP_INDEX_POWERSAVE;
> break;
> default:
> - return sysfs_emit(buf, "%u\n", epp);
> + return -EINVAL;
> }
>
> return sysfs_emit(buf, "%s\n", energy_perf_strings[preference]);
> diff --git a/drivers/cpufreq/amd-pstate.h b/drivers/cpufreq/amd-pstate.h
> index b4c5374762110..b6be2b8fbffbf 100644
> --- a/drivers/cpufreq/amd-pstate.h
> +++ b/drivers/cpufreq/amd-pstate.h
> @@ -108,6 +108,7 @@ struct amd_cpudata {
> u8 epp_default_ac;
> u8 epp_default_dc;
> bool dynamic_epp;
> + bool raw_epp;
> struct notifier_block power_nb;
>
> /* platform profile */
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