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]

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@xxxxxxxxx>
> > > ---
> > >    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