Re: [PATCH] cpufreq/amd-pstate: Fix MinPerf MSR value for performance policy

["Gautham R. Shenoy" <gautham.shenoy@amd.com>]

Hello Juan, Mario,

On Wed, Jan 07, 2026 at 03:24:31PM -0600, Mario Limonciello wrote:
> On 1/7/26 3:19 PM, Juan Martinez wrote:
> > When the CPU frequency policy is set to CPUFREQ_POLICY_PERFORMANCE
> > (which occurs when EPP hint is set to "performance"), the driver
> > incorrectly sets the MinPerf field in CPPC request MSR to nominal_perf
> > instead of lowest_nonlinear_perf.
> > 
> > According to the AMD architectural programmer's manual volume 2 [1],
> > in section "17.6.4.1 CPPC_CAPABILITY_1", lowest_nonlinear_perf represents
> > the most energy efficient performance level (in terms of performance per
> > watt). The MinPerf field should be set to this value even in performance
> > mode to maintain proper power/performance characteristics.
> > 
> > This fixes a regression introduced by commit 0c411b39e4f4c ("amd-pstate: Set
> > min_perf to nominal_perf for active mode performance gov"), which correctly
> > identified that highest_perf was too high but chose nominal_perf as an
> > intermediate value instead of lowest_nonlinear_perf.

> > 
> > The fix changes amd_pstate_update_min_max_limit() to use lowest_nonlinear_perf
> > instead of nominal_perf when the policy is CPUFREQ_POLICY_PERFORMANCE.
> > 
> > [1] https://docs.amd.com/v/u/en-US/24593_3.43
> >      AMD64 Architecture Programmer's Manual Volume 2: System Programming
> >      Section 17.6.4.1 CPPC_CAPABILITY_1
> >      (Referenced in commit 5d9a354cf839a)
> > 
> > Fixes: 0c411b39e4f4c ("amd-pstate: Set min_perf to nominal_perf for active mode performance gov")
> > Tested-by: Kaushik Reddy S <kaushik.reddys@amd.com>
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Juan Martinez <juan.martinez@amd.com>
> 
> I think this change is reasonable, but I'd like to get Gautham's comments as
> the original author of 0c411b39e4f4c.

The active mode performance governor was intended to run the cores at
the highest possible frequency at all times.  Originally the min_perf
was set to max_perf, but we observed frequency throttling in TDP
constrained environments as mentioned in commit 0c411b39e4f4c
("amd-pstate: Set min_perf to nominal_perf for active mode performance
gov"), and as a result min_perf was lowered to nominal_perf so that
the frequency doesn't drop below the nominal_perf as long as the
power/thermal constraints allow it.

This is the behaviour that is desired by customers. So unless you are
observing a performance regression when the min_perf is set to
nominal_perf, I would like to retain this behaviour.

When the governor is switched to "powersave", the min_perf is lowered
to "lowest_nonlinear_perf" by default to match the description in
section 17.6.4.1 CPPC_CAPABILITY_1 of the APM volume 2.

That said, I think we should document this in the code as to why the
min_perf is being set to nominal_perf when
cpudata->policy == CPUFREQ_POLICY_PERFORMANCE.

Juan, do you want to give it a try ?

-- 
Thanks and Regards
gautham.