linux-kernel - Re: [PATCH V7 0/7] amd-pstate preferred core

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Date:   Wed, 20 Sep 2023 21:34:17 +0200
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Huang Rui <ray.huang@....com>, Meng Li <li.meng@....com>,
        Mario Limonciello <mario.limonciello@....com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-acpi@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>,
        linux-kselftest@...r.kernel.org,
        Nathan Fontenot <nathan.fontenot@....com>,
        Deepak Sharma <deepak.sharma@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Shimmer Huang <shimmer.huang@....com>,
        Perry Yuan <Perry.Yuan@....com>,
        Xiaojian Du <Xiaojian.Du@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Borislav Petkov <bp@...en8.de>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH V7 0/7] amd-pstate preferred core

Hello.

On středa 20. září 2023 18:56:09 CEST Mario Limonciello wrote:
> > When applied on top of v6.5.3 this breaks turbo on my 5950X after suspend/resume cycle. Please see the scenario description below.
> > 
> > If I boot v6.5.3 + this patchset, then `turbostat` reports ~4.9 GHz on core 0 where `taskset -c 0 dd if=/dev/zero of=/dev/null` is being run.
> > 
> > After I suspend the machine and then resume it, and run `dd` again, `turbostat` reports the core to be capped to a stock frequency of ~3.4 GHz. Rebooting the machine fixes this, and the CPU can boost again.
> > 
> > If this patchset is reverted, then the CPU can turbo after suspend/resume cycle just fine.
> > 
> > I'm using `amd_pstate=guided`.
> > 
> > Is this behaviour expected?
> 
> To help confirm where the issue is, can I ask you to do three 
> experiments with the patch series applied:
> 
> 1) 'amd_pstate=active' on your kernel command line.

The issue is reproducible. If I toggle the governor in cpupower to `powersave` and back to `performance`, boost is restored.

> 2) 'amd_pstate=active amd_prefcore=disable' on your kernel command line.

The issue is not reproducible.

> 3) 'amd_pstate=guided amd_prefcore=disable' on your kernel command line.

The issue is not reproducible.

I should also mention that in my initial configuration I use `amd_pstate=guided` and `schedutil`. If I switch to `performance` after suspend-resume cycle, the boost is restored. However, if I switch back to `schedutil`, the freq is capped.

Does this info help?

> Looking through the code, I anticipate from your report that it 
> reproduces on "1" but not "2" and "3".
> 
> Meng,
> 
> Can you try to repro?
> 
> I think that it's probably a call to amd_pstate_init_prefcore() missing
> from amd_pstate_cpu_resume() and also amd_pstate_epp_resume().

-- 
Oleksandr Natalenko (post-factum)
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