>>
>> 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)
>>
>> This caused a race condition where the QoS request was added after the
>> initial platform limit update.
>
>To me, the description above is useless for figuring out what's going on, sorry.
>
>This is not a race, but an ordering issue.
>
>The cpufreq driver calls acpi_processor_register_performance(), which
>among other things causes acpi_processor_get_platform_limit() to be
>called, from its ->init() callback which is invoked by the cpufreq
>core before CPUFREQ_CREATE_POLICY notifiers and the policy frequency
>QoS requests are added by acpi_processor_notifier(), so they don't
>exist when acpi_processor_register_performance() gets called and they
>cannot be updated by the acpi_processor_get_platform_limit().
>
>You want them to be updated as soon as they have been added, which is
>kind of reasonable, but it needs to be done only if
>acpi_processor_register_performance() has been called by the cpufreq
>driver.
>
Sorry, I didn't make the question clear.
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 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@xxxxxxxxxx>
>> ---
>> drivers/acpi/processor_perflib.c | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/acpi/processor_perflib.c b/drivers/acpi/processor_perflib.c
>> index 64b8d1e19594..3e7fe95c21d1 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;
>
>So AFAICS this loop needs to check pr->performance in addition to pr.
>
Thanks for the review. I agree and will add a check for pr->performance in v2.
--
lijiayi
