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] [thread-next>] [day] [month] [year] [list]

Message-ID: <59a20c51-aa1a-414d-97a6-610a82947472@kernel.org>
Date: Wed, 19 Mar 2025 11:50:16 -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 3/18/2025 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.

> 
> 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;
>>>>    };
>>>>      /*
>>>
>>
>