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Message-ID: <adccc912-bf93-4320-8011-21c0220c839a@amd.com>
Date: Tue, 11 Feb 2025 10:32:33 +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 04/14] cpufreq/amd-pstate: Overhaul locking
On 2/7/2025 3:26 AM, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@....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. Instead introduce locks into to the
> cpudata structure and lock each CPU independently.
>
> The remaining "global" driver lock is used to ensure that only one
> entity can change driver modes at a given time.
>
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
> drivers/cpufreq/amd-pstate.c | 27 +++++++++++++++++----------
> drivers/cpufreq/amd-pstate.h | 2 ++
> 2 files changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 77bc6418731ee..dd230ed3b9579 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)
> @@ -283,6 +282,8 @@ static int msr_set_epp(struct amd_cpudata *cpudata, u8 epp)
> u64 value, prev;
> int ret;
>
> + lockdep_assert_held(&cpudata->lock);
After making the perf_cached variable writes atomic, do we still need a cpudata->lock ?
Regards,
Dhananjay
> +
> value = prev = READ_ONCE(cpudata->cppc_req_cached);
> value &= ~AMD_CPPC_EPP_PERF_MASK;
> value |= FIELD_PREP(AMD_CPPC_EPP_PERF_MASK, epp);
> @@ -315,6 +316,8 @@ static int shmem_set_epp(struct amd_cpudata *cpudata, u8 epp)
> int ret;
> struct cppc_perf_ctrls perf_ctrls;
>
> + lockdep_assert_held(&cpudata->lock);
> +
> if (epp == cpudata->epp_cached)
> return 0;
>
> @@ -335,6 +338,8 @@ static int amd_pstate_set_energy_pref_index(struct cpufreq_policy *policy,
> struct amd_cpudata *cpudata = policy->driver_data;
> u8 epp;
>
> + guard(mutex)(&cpudata->lock);
> +
> if (!pref_index)
> epp = cpudata->epp_default;
> else
> @@ -750,7 +755,6 @@ 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);
> @@ -973,6 +977,9 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>
> cpudata->cpu = policy->cpu;
>
> + mutex_init(&cpudata->lock);
> + guard(mutex)(&cpudata->lock);
> +
> ret = amd_pstate_init_perf(cpudata);
> if (ret)
> goto free_cpudata1;
> @@ -1179,8 +1186,6 @@ 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;
> @@ -1353,8 +1358,10 @@ 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;
> }
> @@ -1375,7 +1382,6 @@ 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;
> @@ -1472,6 +1478,9 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>
> cpudata->cpu = policy->cpu;
>
> + mutex_init(&cpudata->lock);
> + guard(mutex)(&cpudata->lock);
> +
> ret = amd_pstate_init_perf(cpudata);
> if (ret)
> goto free_cpudata1;
> @@ -1558,6 +1567,8 @@ static int amd_pstate_epp_update_limit(struct cpufreq_policy *policy)
> union perf_cached perf;
> u8 epp;
>
> + guard(mutex)(&cpudata->lock);
> +
> amd_pstate_update_min_max_limit(policy);
>
> if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
> @@ -1646,8 +1657,6 @@ 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 +1693,6 @@ 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);
>
> diff --git a/drivers/cpufreq/amd-pstate.h b/drivers/cpufreq/amd-pstate.h
> index a140704b97430..6d776c3e5712a 100644
> --- a/drivers/cpufreq/amd-pstate.h
> +++ b/drivers/cpufreq/amd-pstate.h
> @@ -96,6 +96,8 @@ struct amd_cpudata {
> bool boost_supported;
> bool hw_prefcore;
>
> + struct mutex lock;
> +
> /* EPP feature related attributes*/
> u8 epp_cached;
> u32 policy;
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