Re: [PATCH v2 3/6] cpufreq: amd_pstate: Add guided autonomous mode

Mario Limonciello
2023-01-13T06:03:16Z

On 1/12/23 23:21, Wyes Karny wrote:
> From ACPI spec below 3 modes for CPPC can be defined:
> 1. Non autonomous: OS scaling governor specifies operating frequency/
> performance level through `Desired Performance` register and platform
> follows that.
> 2. Guided autonomous: OS scaling governor specifies min and max
> frequencies/ performance levels through `Minimum Performance` and
> `Maximum Performance` register, and platform can autonomously select an
> operating frequency in this range.
> 3. Fully autonomous: OS only hints (via EPP) to platform for the required
> energy performance preference for the workload and platform autonomously
> scales the frequency.
>
> Currently (1) is supported by amd_pstate as passive mode, and (3) is
> implemented by EPP support. This change is to support (2).
>
> In guided autonomous mode the min_perf is based on the input from the
> scaling governor. For example, in case of schedutil this value depends
> on the current utilization. And max_perf is set to max capacity.
>
> To activate guided auto mode ``amd_pstate=guided`` command line
> parameter has to be passed in the kernel.
>
> Signed-off-by: Wyes Karny <wyes.karny@amd.com>
> ---
> .../admin-guide/kernel-parameters.txt | 15 ++++++----
> drivers/cpufreq/amd-pstate.c | 29 ++++++++++++++++---
> include/linux/amd-pstate.h | 2 ++
> 3 files changed, 37 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index e3618dfdb36a..0d8486325c9a 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -7015,11 +7015,11 @@
> Do not enable amd_pstate as the default
> scaling driver for the supported processors
> passive
> - Use amd_pstate as a scaling driver, driver requests a
> - desired performance on this abstract scale and the power
> - management firmware translates the requests into actual
> - hardware states (core frequency, data fabric and memory
> - clocks etc.)
> + Use amd_pstate with passive mode as a scaling driver.
> + In this mode autonomous selection is disabled.
> + Driver requests a desired performance level and platform
> + tires to match the same performance level (if it is
> + satisfied by guaranteed performance level).
> active
> Use amd_pstate_epp driver instance as the scaling driver,
> driver provides a hint to the hardware if software wants
> @@ -7027,3 +7027,8 @@
> to the CPPC firmware. then CPPC power algorithm will
> calculate the runtime workload and adjust the realtime cores
> frequency.
> + guided
> + Activate guided autonomous mode. Driver requests minimum and
> + maximum performance level and the platform autonomously
> + selects a performance level in this range and appropriate
> + to the current workload.
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 87450413cf45..20d78dad712d 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -267,6 +267,20 @@ static int cppc_init_perf(struct amd_cpudata *cpudata)
> cppc_perf.lowest_nonlinear_perf);
> WRITE_ONCE(cpudata->lowest_perf, cppc_perf.lowest_perf);
>
> + ret = cppc_get_auto_sel_caps(cpudata->cpu, &cppc_perf);
> + if (ret) {
> + pr_warn("failed to get auto_sel\n");

To make debugging easier in the future perhaps:

pr_warn("failed to get auto sel: %d\n", ret);

> + return 0;
> + }
> +
> + if (cppc_state == AMD_PSTATE_PASSIVE)
> + ret = cppc_set_auto_sel(cpudata->cpu, 0);
> + else if (cppc_state == AMD_PSTATE_GUIDED)
> + ret = cppc_set_auto_sel(cpudata->cpu, 1);
> +

as a simplification maybe:

ret = cppc_set_auto_sel(cpudata->cpu, cppc_state == AMD_PSTATE_PASSIVE ?
0 : 1);

> + if (ret)
> + pr_warn("failed to set auto_sel\n");

Again, probably good to emit the error code in this message;
> +
> return 0;

As this could fail now shouldn't you be returning ret?

> }
>
> @@ -344,12 +358,18 @@ static inline bool amd_pstate_sample(struct amd_cpudata *cpudata)
> }
>
> static void amd_pstate_update(struct amd_cpudata *cpudata, u32 min_perf,
> - u32 des_perf, u32 max_perf, bool fast_switch)
> + u32 des_perf, u32 max_perf, bool fast_switch, int guv_flags)
> {
> u64 prev = READ_ONCE(cpudata->cppc_req_cached);
> u64 value = prev;
>
> des_perf = clamp_t(unsigned long, des_perf, min_perf, max_perf);
> +
> + if ((cppc_state == AMD_PSTATE_GUIDED) && (guv_flags & CPUFREQ_GOV_DYNAMIC_SWITCHING)) {
> + min_perf = des_perf;
> + des_perf = 0;
> + }
> +
> value &= ~AMD_CPPC_MIN_PERF(~0L);
> value |= AMD_CPPC_MIN_PERF(min_perf);
>
> @@ -404,7 +424,7 @@ static int amd_pstate_target(struct cpufreq_policy *policy,
>
> cpufreq_freq_transition_begin(policy, &freqs);
> amd_pstate_update(cpudata, min_perf, des_perf,
> - max_perf, false);
> + max_perf, false, policy->governor->flags);
> cpufreq_freq_transition_end(policy, &freqs, false);
>
> return 0;
> @@ -438,7 +458,8 @@ static void amd_pstate_adjust_perf(unsigned int cpu,
> if (max_perf < min_perf)
> max_perf = min_perf;
>
> - amd_pstate_update(cpudata, min_perf, des_perf, max_perf, true);
> + amd_pstate_update(cpudata, min_perf, des_perf, max_perf, true,
> + policy->governor->flags);
> cpufreq_cpu_put(policy);
> }
>
> @@ -1233,7 +1254,7 @@ static int __init amd_pstate_init(void)
> /* capability check */
> if (boot_cpu_has(X86_FEATURE_CPPC)) {
> pr_debug("AMD CPPC MSR based functionality is supported\n");
> - if (cppc_state == AMD_PSTATE_PASSIVE)
> + if (cppc_state != AMD_PSTATE_ACTIVE)
> default_pstate_driver->adjust_perf = amd_pstate_adjust_perf;
> } else {
> pr_debug("AMD CPPC shared memory based functionality is supported\n");
> diff --git a/include/linux/amd-pstate.h b/include/linux/amd-pstate.h
> index 15761a581e82..e07cfbd63560 100644
> --- a/include/linux/amd-pstate.h
> +++ b/include/linux/amd-pstate.h
> @@ -92,6 +92,7 @@ enum amd_pstate_mode {
> AMD_PSTATE_DISABLE = 0,
> AMD_PSTATE_PASSIVE,
> AMD_PSTATE_ACTIVE,
> + AMD_PSTATE_GUIDED,
> AMD_PSTATE_MAX,
> };
>
> @@ -99,6 +100,7 @@ static const char * const amd_pstate_mode_string[] = {
> [AMD_PSTATE_DISABLE] = "disable",
> [AMD_PSTATE_PASSIVE] = "passive",
> [AMD_PSTATE_ACTIVE] = "active",
> + [AMD_PSTATE_GUIDED] = "guided",
> NULL,
> };
>