Re: [PATCH v5 4/7] cpufreq: amd_pstate: fix wrong lowest perf fetch

Punit Agrawal
2022-09-01T14:59:03Z

"Yuan, Perry" <Perry.Yuan@amd.com> writes:

[...]

>> Perry Yuan <Perry.Yuan@amd.com> writes:
>>
>> > Fix the wrong lowest perf value reading which is used for new des_perf
>> > calculation by governor requested, the incorrect min_perf will get
>> > incorrect des_perf to be set , that will cause the system frequency
>> > changing unexpectedly.
>> >
>> > Reviewed-by: Huang Rui <ray.huang@amd.com>
>> > Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
>> > Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
>> > Signed-off-by: Su Jinzhou <jinzhou.su@amd.com>
>> > ---
>> > drivers/cpufreq/amd-pstate.c | 2 +-
>> > 1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/cpufreq/amd-pstate.c
>> > b/drivers/cpufreq/amd-pstate.c index 5cdef6638681..183cdd4ba00e 100644
>> > --- a/drivers/cpufreq/amd-pstate.c
>> > +++ b/drivers/cpufreq/amd-pstate.c
>> > @@ -307,7 +307,7 @@ static int amd_pstate_target(struct cpufreq_policy
>> *policy,
>> > return -ENODEV;
>> >
>> > cap_perf = READ_ONCE(cpudata->highest_perf);
>> > - min_perf = READ_ONCE(cpudata->lowest_nonlinear_perf);
>> > + min_perf = READ_ONCE(cpudata->lowest_perf);
>> > max_perf = cap_perf;
>> >
>> > freqs.old = policy->cur;
>>
>> This looks to be a pretty big change (lowest nonlinear vs lowest). Does the patch
>> need to be backported to older kernels?
>
> The patch fixes the min perf initial value, the correct min perf is lowest_perf which is captured through MSR_AMD_CPPC_CAP1 register or the cppc_get_perf_caps().
> Yes, the patch will need to be backported to other kernel branch as issue fix.

Great, thanks for confirming! …