Re: [PATCH v5 0/2] cpufreq: acpi-cpufreq: fix P-state index mismatch between perf->states[] and freq_table[]

[Rafael J. Wysocki (Intel)]

On Fri, Nov 6, 2026 at 7:40 PM lirongqing <lirongqing@xxxxxxxxx> wrote:
>
> From: Li RongQing <lirongqing@xxxxxxxxx>
>
> policy->freq_table is built by filtering out _PSS entries that are not
> lower in frequency than the previous one, and the original ACPI P-state
> index of each remaining entry is kept in freq_table[].driver_data.  The
> index spaces of perf->states[] and freq_table[] therefore differ, and
> mixing them up leads to the frequency of one P-state being attributed to
> another.
>
> Patch 1/2 is unchanged from v4 and fixes the cached frequency used by
> get_cur_freq_on_cpu() to detect a firmware frequency change behind the
> OS's back.
>
> Patch 2/2 is new in v5.  As Rafael pointed out, Sashiko observed that
> the extract_msr() fallback interferes with 1/2 and can render it
> ineffective: when the status read from the hardware matches no
> freq_table entry, extract_msr() returns freq_table[0].frequency instead
> of reporting the status as unknown.  If the OS is already at the P-state
> corresponding to freq_table[0], a firmware switch to a filtered-out
> P-state then compares equal to the cached frequency, data->resume is
> left clear and the next ->target() call does not rewrite the control
> register.  So 1/2 alone does not make the detection work in that case,
> and the two patches are posted together rather than separately as I had
> suggested earlier.
>
> v4: https://lkml.iu.edu/2609.1/07369.html
>
> Changes since v4:
>  - Drop "cpufreq: acpi-cpufreq: fix P-state index mismatch in
>    extract_io()", which has been applied.  This series is based on top
>    of it.
>  - Add 2/2 to stop extract_msr() from masking firmware P-state changes,
>    as reported by Sashiko, and note the dependency in 1/2's changelog.

So Sashiko has feedback on this one now:

https://sashiko.dev/#/message/20261106184008.1728-2-lirongqing%40baidu.com

>  - 1/2: no functional change; changelog extended to say that it fixes
>    only the cached side of the comparison, and a duplicate
>    Signed-off-by was removed.
>
> Li RongQing (2):
>   cpufreq: acpi-cpufreq: fix P-state index mismatch in
>     get_cur_freq_on_cpu()
>   cpufreq: acpi-cpufreq: don't mask firmware P-state changes
>
>  drivers/cpufreq/acpi-cpufreq.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> --
> 2.9.4
>