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

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Message-ID: <9665af79-d439-e05a-5333-62f71a2ac55c@linux.intel.com>
Date:   Mon, 28 Aug 2023 16:35:13 -0700
From:   Keyon Jie <yang.jie@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Doug Smythies <dsmythies@...us.net>, gregkh@...uxfoundation.org
Cc:     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 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 When the CPU frequency is outdated arch_freq_get_on_cpu()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.

Thanks,
~Keyon