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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <43daf20e-0d5b-4a1e-8179-bb2af39f512f@amd.com>
Date: Wed, 19 Mar 2025 12:13:53 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Mario Limonciello <superm1@...nel.org>,
 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>
Subject: Re: [PATCH v2 1/5] cpufreq/amd-pstate: Add dynamic energy performance
 preference

On 3/19/2025 11:50, Mario Limonciello wrote:
> On 3/18/2025 22:43, Dhananjay Ugwekar wrote:
>> On 3/19/2025 1:06 AM, Mario Limonciello wrote:
>>> 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));
>>             ^^^^^^^^^^^^ (mentioned below)
>>>          if (ret)
>>>
>>> Thoughts?
>>
>> Yes, this looks good, because anyway there is no point in having 
>> performance governor and dynamic
>> epp set at the same time.
>>
>> I found one related quirk though, we are setting performance governor 
>> for server platforms in
>> amd_pstate_epp_cpu_init() and then setting epp at the line highlighted 
>> above. We dont have a
>> check in *_set_epp() functions for performance governor. This could 
>> alter the performance governor
>> behavior if we set a "balanced" epp for it. I haven't tested this part 
>> yet.
> 
> In that case we probably want the "default" ACPI platform profile to be 
> "performance" when on a server instead of balanced.

Actually this is already done:

		cpudata->current_profile = PLATFORM_PROFILE_PERFORMANCE;

I'll post an updated patch series for you to test.

> 
>>
>> Thanks,
>> Dhananjay
>>
>>>
>>>>> +
>>>>>        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;
>>>>>    };
>>>>>      /*
>>>>
>>>
>>
>