Re: 答复: [外部邮件] Re: [PATCH v2 1/2] cpufreq: acpi-cpufreq: fix P-state index mismatch in extract_io()

[Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>]

On 8/18/2026 2:46 PM, Li,Rongqing wrote:
>>> When policy->freq_table is built in acpi_cpufreq_cpu_init(), entries
>>> with duplicate frequencies are skipped. The original P-state index for
>>> each remaining entry is stored in freq_table[].driver_data, so the
>>> index space of freq_table no longer matches perf->states[].
>>>
>>> extract_io() walks perf->states[] with index i and uses the same i to
>>> index policy->freq_table[i]. This causes two problems when duplicate
>>> frequencies exist:
>>>
>>>     - Returning the frequency of the wrong P-state
>>>     - Returning 0 from a zeroed tail entry, or even CPUFREQ_TABLE_END
>>>       (~1u) reported as 0xfffffffe kHz
>>
>> AFAICT, It may be worth expanding the changelog to cover the consequences
>> described below , particularly the resulting divergence between the hardware
>> state and the cpufreq core's view of the current
>> frequency:
>>
>> Furthermore, extract_io() is only reachable on ACPI_ADR_SPACE_SYSTEM_IO
>> platforms, where cpufreq_driver->get is not installed, so its only caller in
>> practice is check_freqs(), i.e. only when the acpi_pstate_strict module
>> parameter is set.
>>
>> There, the mismatched lookup makes the frequency comparison fail even
>> though drv_write() has already switched the hardware to the requested P-state.
>> So check_freqs() sleeps through all 100 iterations - at least
>> ~1 ms of usleep_range() plus 100 cross-CPU calls and I/O port reads, all with
>> policy->rwsem held - and ->target_index() returns -EAGAIN. perf
>> ->state is therefore left at its previous value while the hardware sits
>> at the new one.
>>
>> The core then restores policy->cur to the old frequency, and because
>> __cpufreq_driver_target() returns early when the requested frequency equals
>> policy->cur, the driver is not called again for it - so the control register is not
>> rewritten and the CPU is left running at a frequency the core does not know
>> about.
>>
>>
>>>
>>> Fix it by walking policy->freq_table with cpufreq_for_each_entry() and
>>> using perf->states[pos->driver_data].status, aligning with extract_msr().
>>>
>>> Fixes: 8cee1eed8e78 ("cpufreq: ACPI: Remove freq_table from
>>> acpi_cpufreq_data")
>>
>> The real tag should be fe27cb358835 ("[CPUFREQ][2/8] acpi:
>> reorganize code to make MSR support addition easier")
>>
>> That commit added both the entry-skipping loop with the freq_table[].index
>> (now .driver_data) back-pointer, which is what makes the two indices diverge,
>> and the faulty lookup itself -- back then in a function called extract_freq().
>> dde9f7ba60ad ("[CPUFREQ][3/8] acpi
>> cpufreq: Pull in MSR based transition support") merely renamed it to
>> extract_io().
>>
> 
> Thanks, I will send v3

Thanks, I will review the patch v2 2/2

> 
> [Li,Rongqing]
> 
> 
>>
>>> Signed-off-by: Li RongQing <lirongqing@baidu.com>
>>> ---
>>>    drivers/cpufreq/acpi-cpufreq.c | 9 ++++-----
>>>    1 file changed, 4 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/cpufreq/acpi-cpufreq.c
>>> b/drivers/cpufreq/acpi-cpufreq.c index 21639d9..1abe9ab 100644
>>> --- a/drivers/cpufreq/acpi-cpufreq.c
>>> +++ b/drivers/cpufreq/acpi-cpufreq.c
>>> @@ -197,14 +197,13 @@ static unsigned extract_io(struct cpufreq_policy
>> *policy, u32 value)
>>>    {
>>>    	struct acpi_cpufreq_data *data = policy->driver_data;
>>>    	struct acpi_processor_performance *perf;
>>> -	int i;
>>> +	struct cpufreq_frequency_table *pos;
>>>
>>>    	perf = to_perf_data(data);
>>>
>>> -	for (i = 0; i < perf->state_count; i++) {
>>> -		if (value == perf->states[i].status)
>>> -			return policy->freq_table[i].frequency;
>>> -	}
>>> +	cpufreq_for_each_entry(pos, policy->freq_table)
>>> +		if (value == perf->states[pos->driver_data].status)
>>> +			return pos->frequency;
>>>    	return 0;
>>>    }
>>>
>>
>>
>> --
>> Thx and BRs,
>> Zhongqiu Han
> 


-- 
Thx and BRs,
Zhongqiu Han