Re: [PATCH 04/14] cpufreq/amd-pstate: Overhaul locking

[Dhananjay Ugwekar <Dhananjay.Ugwekar@amd.com>]

On 2/7/2025 3:26 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.  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@amd.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;