Re: [PATCH 6/8] cpufreq: amd-pstate: Merge amd_pstate_highest_perf_set() into amd_get_boost_ratio_numerator()

Gautham R. Shenoy
2024-08-28T06:00:01Z

On Tue, Aug 27, 2024 at 01:36:47PM -0500, Mario Limonciello wrote:
> On 8/27/2024 11:52, Gautham R. Shenoy wrote:

[..snip..]

> >
> >
> > So henceforth, cpudata->highest_perf is expected to cache the value of
> > CPPC.highest_perf and not the boost_ratio_numerator. There are couple
> > of user-visible changes due to this.
> >
> >
> > 1. On platforms where preferred-core is supported, previously the
> > sysfs file
> > /sys/devices/system/cpu/cpuX/cpufreq/amd_pstate_highest_perf would
> > report the boost_ratio_numerator. Henceforth it will report
> > CPPC.highest_perf.

One other side effect is that the highest_perf sysfs file will now
reveal the differential highest_perf, even when "amd_prefcore=false",
while earlier all the cores would report CPPC_HIGHEST_PERF_DEFAULT.

I think we may be better off reporting the boost-numerator here, but
that's really not the highest_perf :(

> >
> > I hope there are no userspace tools that compute the boost_ratio
> > using the syfs amd_pstate_highest_perf/amd_pstate_nominal_perf.
> >
> > 2. The amd_pstate_prefcore_ranking and amd_pstate_highest_perf will
> > show the same values on all platforms, and henceforth are
> > redundant.
> >
>
> Good observations here. I'm not aware of any tools trying to replicate this
> calculation.
> With the redundancy I would actually argue we should just drop the sysfs
> file 'amd_pstate_prefcore_ranking'.
>
> Thoughts?

Looking at the code again, I realize that I was
wrong. cpudata->prefcore_ranking also gets updated in
amd_pstate_update_min_max_limits() and reflects the dynamic
preference.

While cpudata->highest_perf value indicates the initial boot-time
preference.

Hence it makes sense to amd_pstate_prefcore_ranking.

>
> >
> > Shouldn't this be documented?
>
> I noticed amd_pstate_prefcore_ranking wasn't properly documented in
> amd-pstate.rst in the first place. If the decision is not to drop the sysfs
> file, then I'll add a section for it.

Thanks.

>
> >
> > The rest of the patch looks good to me.
> >
> >
> >
--
Thanks and Regards
gautham.