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

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Message-ID: <6ae8f24e-494f-480d-9d5f-4100f50a6b63@amd.com>
Date: Mon, 24 Feb 2025 10:53:15 +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 05/19] cpufreq/amd-pstate: Overhaul locking

On 2/20/2025 2:32 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.  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@....com>

> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>
> Signed-off-by: Mario Limonciello <mario.limonciello@....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);
>