linux-kernel - Re: [PATCH v2] ACPI: Fix initial QoS constraint application order in PPC initialization

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Message-ID: <4697e3bd-9954-45af-a4a4-e542760102d7@kylinos.cn>
Date: Wed, 23 Jul 2025 15:05:56 +0800
From: 李佳怡 <lijiayi@...inos.cn>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: rafael@...nel.org, jiayi_dec@....com, lenb@...nel.org,
 linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ACPI: Fix initial QoS constraint application order in
 PPC initialization



在 2025/7/21 21:27, Rafael J. Wysocki 写道:
> On Mon, Jul 21, 2025 at 5:26 AM Jiayi Li <lijiayi@...inos.cn> wrote:
>>
>> This patch fixes an issue where _PPC frequency limits set by the BIOS
>> failed to take effect due to incorrect call ordering. Previously,
>> freq_qos_update_request() was being called before freq_qos_add_request(),
>> causing the constraint updates to be ignored. With this fix, the frequency
>> limits are now properly enforced as intended.
>> The original initialization sequence was:
>>
>> cpufreq_policy_online()
>>      acpi_cpufreq_cpu_init()
>>          acpi_processor_get_platform_limit()
>>              freq_qos_update_request(&perflib_req)
>>      blocking_notifier_call_chain(...)
>>          acpi_processor_ppc_init()
>>              freq_qos_add_request(&perflib_req)
>>
>> The new sequence explicitly ensures:
>>
>> cpufreq_policy_online()
>>      acpi_cpufreq_cpu_init()
>>          acpi_processor_get_platform_limit()
>>              freq_qos_update_request(&perflib_req)
>>      blocking_notifier_call_chain(...)
>>          acpi_processor_ppc_init()
>>              freq_qos_add_request(&perflib_req)
>> +           acpi_processor_get_platform_limit()
>> +               freq_qos_update_request(&perflib_req)
>>
>> The critical change adds an immediate platform limit update after the
>> QoS request is registered. This guarantees that the initial P-state
>> constraint is applied before any subsequent updates, resolving the window
>> where constraints could be applied out-of-order.
>>
>> Fixes: d15ce412737a ("ACPI: cpufreq: Switch to QoS requests instead of cpufreq notifier")
>> Signed-off-by: Jiayi Li <lijiayi@...inos.cn>
>> ---
>> v1 -> v2:
>> - Modify the commit.
>> - Add pr->performance check in acpi_processor_ppc_init loop.
>> ---
>> ---
>>   drivers/acpi/processor_perflib.c | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/acpi/processor_perflib.c b/drivers/acpi/processor_perflib.c
>> index 64b8d1e19594..56f2b8354d62 100644
>> --- a/drivers/acpi/processor_perflib.c
>> +++ b/drivers/acpi/processor_perflib.c
>> @@ -173,6 +173,9 @@ void acpi_processor_ppc_init(struct cpufreq_policy *policy)
>>   {
>>          unsigned int cpu;
>>
>> +       if (ignore_ppc == 1)
>> +               return;
>> +
>>          for_each_cpu(cpu, policy->related_cpus) {
>>                  struct acpi_processor *pr = per_cpu(processors, cpu);
>>                  int ret;
>> @@ -180,6 +183,9 @@ void acpi_processor_ppc_init(struct cpufreq_policy *policy)
>>                  if (!pr)
>>                          continue;
>>
>> +               if (!pr->performance)
>> +                       continue;
>> +
>>                  /*
>>                   * Reset performance_platform_limit in case there is a stale
>>                   * value in it, so as to make it match the "no limit" QoS value
> 
> Applied, but I have consolidated the pr and pr->performance checks above.
> 
> I have also made some changes in the subject and changelog.
> 
> Thanks!

Thanks for the review!

> 
>> @@ -193,6 +199,11 @@ void acpi_processor_ppc_init(struct cpufreq_policy *policy)
>>                  if (ret < 0)
>>                          pr_err("Failed to add freq constraint for CPU%d (%d)\n",
>>                                 cpu, ret);
>> +
>> +               ret = acpi_processor_get_platform_limit(pr);
>> +               if (ret)
>> +                       pr_err("Failed to update freq constraint for CPU%d (%d)\n",
>> +                              cpu, ret);
>>          }
>>   }
>>
>> --