linux-kernel - Re: [PATCH v2] cpufreq: intel_pstate: set stale CPU frequency to minimum

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Date:   Tue, 5 Sep 2023 15:23:41 -0700
From:   Keyon Jie <yang.jie@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Doug Smythies <dsmythies@...us.net>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] cpufreq: intel_pstate: set stale CPU frequency to
 minimum

On 9/5/23 11:30, Rafael J. Wysocki wrote:
> On Tue, Sep 5, 2023 at 8:17 PM Keyon Jie <yang.jie@...ux.intel.com> wrote:
>>
>>
>>
>> On 8/29/23 01:57, Greg KH wrote:
>>> On Mon, Aug 28, 2023 at 04:35:13PM -0700, Keyon Jie wrote:
>>>>
>>>>
>>>> On 8/22/23 04:46, Rafael J. Wysocki wrote:
>>>>> On Sun, Aug 20, 2023 at 10:46 PM Doug Smythies <dsmythies@...us.net> wrote:
>>>>>>
>>>>>> The intel_pstate CPU frequency scaling driver does not
>>>>>> use policy->cur and it is 0.
>>>>>> When the CPU frequency is outdated arch_freq_get_on_cpu()
>>>>>> will default to the nominal clock frequency when its call to
>>>>>> cpufreq_quick_getpolicy_cur returns the never updated 0.
>>>>>> Thus, the listed frequency might be outside of currently
>>>>>> set limits. Some users are complaining about the high
>>>>>> reported frequency, albeit stale, when their system is
>>>>>> idle and/or it is above the reduced maximum they have set.
>>>>>>
>>>>>> This patch will maintain policy_cur for the intel_pstate
>>>>>> driver at the current minimum CPU frequency.
>>>>>>
>>>>>> Reported-by: Yang Jie <yang.jie@...ux.intel.com>
>>>>>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217597
>>>>>> Signed-off-by: Doug Smythies <dsmythies@...us.net>
>>>>>> ---
>>>>>>
>>>>>> v1 -> v2:
>>>>>>       * v1 was a completely different approach, programming around
>>>>>>         the issue rather than fixing it at the source.
>>>>>>         reference:
>>>>>>         https://patchwork.kernel.org/project/linux-pm/patch/006901d9be8c$f4439930$dccacb90$@telus.net/
>>>>>>       * v2 does not fix an issue with the intel_cpufreq CPU scaling
>>>>>>         driver (A.K.A. the intel_pstate driver in passive mode) and
>>>>>>         the schedutil CPU frequency scaling governor when HWP is enabled
>>>>>>         where limit changes are not reflected in the stale listed frequencies.
>>>>>>         A fix for that will be some future patch.
>>>>>>
>>>>>> ---
>>>>>>     drivers/cpufreq/intel_pstate.c | 5 +++++
>>>>>>     1 file changed, 5 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
>>>>>> index 8ca2bce4341a..08284dee583a 100644
>>>>>> --- a/drivers/cpufreq/intel_pstate.c
>>>>>> +++ b/drivers/cpufreq/intel_pstate.c
>>>>>> @@ -2609,6 +2609,11 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
>>>>>>                            intel_pstate_clear_update_util_hook(policy->cpu);
>>>>>>                    intel_pstate_hwp_set(policy->cpu);
>>>>>>            }
>>>>>> +       /* policy current is never updated with the intel_pstate driver
>>>>>> +        * but it is used as a stale frequency value. So, keep it within
>>>>>> +        * limits.
>>>>>> +        */
>>>>>> +       policy->cur = policy->min;
>>>>>>
>>>>>>            mutex_unlock(&intel_pstate_limits_lock);
>>>>>>
>>>>>> --
>>>>>
>>>>> Applied as 6.6 material, with some mailer-induced white space damage
>>>>> fixed and the new comment adjusted to the kernel coding style.
>>>>>
>>>>> Thanks!
>>>>
>>>> Hi Doug and Rafael,
>>>>
>>>> Thank you for making the fix happen.
>>>>
>>>> Hi Greg,
>>>>
>>>> Will this be picked to the stable linux-6.1.y and linux-6.4.y kernel, it
>>>> could benefit to users there.
>>>
>>> Sure, when it hits Linus's tree, please follow the instructions in:
>>>       https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
>>> for how to get it merged.
>>
>> Thank you Greg.
>>
>> Hi Rafael,
>>
>> As the issue happens from the 5.18 onward kernels, we need the fix to be
>> picked for stable kernels after that, could you please help to add "Cc:
>> stable@...r.kernel.org" in the sign-off area when you send it to the
>> mainline?
> 
> It's already merged, as commit d51847acb018 ("cpufreq: intel_pstate:
> set stale CPU frequency to minimum").
> 
> Please feel free to send an inclusion request for it to stable@...r.kernel.org

Thank you Rafael, will do.

Thanks,
~Keyon

> 
> Thanks!