Re: [PATCH v4 05/19] cpufreq/amd-pstate: Overhaul locking

Dhananjay Ugwekar
2025-02-24T05:23:27Z

On 2/20/2025 2:32 AM, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@amd.com>
>
> amd_pstate_cpu_boost_update() and refresh_frequency_limits() both
> update the policy state and have nothing to do with the amd-pstate
> driver itself.
>
> A global "limits" lock doesn't make sense because each CPU can have
> policies changed independently. Each time a CPU changes values they
> will atomically be written to the per-CPU perf member. Drop per CPU
> locking cases.
>
> The remaining "global" driver lock is used to ensure that only one
> entity can change driver modes at a given time.
>

Reviewed-by: Dhananjay Ugwekar <dhananjay.ugwekar@amd.com>

> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
> drivers/cpufreq/amd-pstate.c | 13 +++----------
> 1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index a6066fb4ffb63..85e3daddb56e0 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -196,7 +196,6 @@ static inline int get_mode_idx_from_str(const char *str, size_t size)
> return -EINVAL;
> }
>
> -static DEFINE_MUTEX(amd_pstate_limits_lock);
> static DEFINE_MUTEX(amd_pstate_driver_lock);
>
> static u8 msr_get_epp(struct amd_cpudata *cpudata)
> @@ -752,7 +751,6 @@ static int amd_pstate_set_boost(struct cpufreq_policy *policy, int state)
> pr_err("Boost mode is not supported by this processor or SBIOS\n");
> return -EOPNOTSUPP;
> }
> - guard(mutex)(&amd_pstate_driver_lock);
>
> ret = amd_pstate_cpu_boost_update(policy, state);
> refresh_frequency_limits(policy);
> @@ -1175,8 +1173,6 @@ static ssize_t store_energy_performance_preference(
> if (ret < 0)
> return -EINVAL;
>
> - guard(mutex)(&amd_pstate_limits_lock);
> -
> ret = amd_pstate_set_energy_pref_index(policy, ret);
>
> return ret ? ret : count;
> @@ -1349,8 +1345,10 @@ int amd_pstate_update_status(const char *buf, size_t size)
> if (mode_idx < 0 || mode_idx >= AMD_PSTATE_MAX)
> return -EINVAL;
>
> - if (mode_state_machine[cppc_state][mode_idx])
> + if (mode_state_machine[cppc_state][mode_idx]) {
> + guard(mutex)(&amd_pstate_driver_lock);
> return mode_state_machine[cppc_state][mode_idx](mode_idx);
> + }
>
> return 0;
> }
> @@ -1371,7 +1369,6 @@ static ssize_t status_store(struct device *a, struct device_attribute *b,
> char *p = memchr(buf, '\n', count);
> int ret;
>
> - guard(mutex)(&amd_pstate_driver_lock);
> ret = amd_pstate_update_status(buf, p ? p - buf : count);
>
> return ret < 0 ? ret : count;
> @@ -1643,8 +1640,6 @@ static int amd_pstate_epp_cpu_offline(struct cpufreq_policy *policy)
> if (cpudata->suspended)
> return 0;
>
> - guard(mutex)(&amd_pstate_limits_lock);
> -
> if (trace_amd_pstate_epp_perf_enabled()) {
> trace_amd_pstate_epp_perf(cpudata->cpu, perf.highest_perf,
> AMD_CPPC_EPP_BALANCE_POWERSAVE,
> @@ -1684,8 +1679,6 @@ static int amd_pstate_epp_resume(struct cpufreq_policy *policy)
> struct amd_cpudata *cpudata = policy->driver_data;
>
> if (cpudata->suspended) {
> - guard(mutex)(&amd_pstate_limits_lock);
> -
> /* enable amd pstate from suspend state*/
> amd_pstate_epp_reenable(policy);
>