linux-kernel - Re: [PATCH v2 1/5] cpufreq/amd-pstate: Add dynamic energy performance preference

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Message-ID: <4e0ab8ce-908e-49a1-8445-14129a41afda@kernel.org>
Date: Tue, 18 Mar 2025 14:36:10 -0500
From: Mario Limonciello <superm1@...nel.org>
To: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>,
 "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 v2 1/5] cpufreq/amd-pstate: Add dynamic energy performance
 preference

On 3/12/2025 07:16, Dhananjay Ugwekar wrote:
> On 3/4/2025 8:53 PM, Mario Limonciello wrote:
>> From: Mario Limonciello <mario.limonciello@....com>
>>
>> Dynamic energy performance preference will change the EPP profile
>> based on whether the machine is running on AC or DC power.
>>
>> A notification chain from the power supply core is used to adjust
>> EPP values on plug in or plug out events.
>>
>> For non-server systems:
>>      * the default EPP for AC mode is `performance`.
>>      * the default EPP for DC mode is `balance_performance`.
>>
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>> ---
>> v1->v2:
>>   * Change defaults to performance (AC) and balance_performance (DC)
>>   * Default Kconfig to disabled for now
>>   * Rebase on latest branch
>> ---
>>   Documentation/admin-guide/pm/amd-pstate.rst |  18 ++-
>>   drivers/cpufreq/Kconfig.x86                 |  12 ++
>>   drivers/cpufreq/amd-pstate.c                | 129 ++++++++++++++++++--
>>   drivers/cpufreq/amd-pstate.h                |   5 +-
>>   4 files changed, 155 insertions(+), 9 deletions(-)
>>
> [Snip]
>> @@ -1556,6 +1667,10 @@ static int amd_pstate_epp_set_policy(struct cpufreq_policy *policy)
>>   	if (!policy->cpuinfo.max_freq)
>>   		return -ENODEV;
>>   
>> +	/* policy can't be changed to performance policy while dynamic epp is enabled */
>> +	if (policy->policy == CPUFREQ_POLICY_PERFORMANCE && cpudata->dynamic_epp)
>> +		return -EBUSY;
> 
> We might need to tweak this condition, because if we enable "CONFIG_X86_AMD_PSTATE_DYNAMIC_EPP" in config
> and boot with "amd_pstate=active" it lands here (cpufreq_online()->amd_pstate_epp_set_policy()) driver init fails
> as the default governor is performance.
> 

The check is important to make sure that you can't go to performance 
mode after init.

I think this is the way I would want to solve it.
Set policy to powersave before enabling dynamic epp for 
amd_pstate_epp_cpu_init().

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 824756ac0010e..4a0f561d0e2d1 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1729,8 +1729,10 @@ static int amd_pstate_epp_cpu_init(struct 
cpufreq_policy *policy)
                 WRITE_ONCE(cpudata->cppc_req_cached, value);
         }

-       if (dynamic_epp)
+       if (dynamic_epp) {
+               policy->policy = CPUFREQ_POLICY_POWERSAVE;
                 ret = amd_pstate_set_dynamic_epp(policy);
+       }
         else
                 ret = amd_pstate_set_epp(policy, 
amd_pstate_get_balanced_epp(policy));
         if (ret)

Thoughts?

>> +
>>   	cpudata->policy = policy->policy;
>>   
>>   	ret = amd_pstate_epp_update_limit(policy);
>> diff --git a/drivers/cpufreq/amd-pstate.h b/drivers/cpufreq/amd-pstate.h
>> index fbe1c08d3f061..6882876f895de 100644
>> --- a/drivers/cpufreq/amd-pstate.h
>> +++ b/drivers/cpufreq/amd-pstate.h
>> @@ -104,7 +104,10 @@ struct amd_cpudata {
>>   	/* EPP feature related attributes*/
>>   	u32	policy;
>>   	bool	suspended;
>> -	u8	epp_default;
>> +	u8	epp_default_ac;
>> +	u8	epp_default_dc;
>> +	bool	dynamic_epp;
>> +	struct notifier_block power_nb;
>>   };
>>   
>>   /*
>