Message-ID: <5973628.lOV4Wx5bFT@natalenko.name>
Date:   Tue, 19 Sep 2023 21:01:20 +0200
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Huang Rui <ray.huang@....com>, Meng Li <li.meng@....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>,
        Mario Limonciello <mario.limonciello@....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>, Meng Li <li.meng@....com>
Subject: Re: [PATCH V7 0/7] amd-pstate preferred core

Hello.

On pondělí 18. září 2023 10:14:00 CEST Meng Li wrote:
> Hi all:
> 
> The core frequency is subjected to the process variation in semiconductors.
> Not all cores are able to reach the maximum frequency respecting the
> infrastructure limits. Consequently, AMD has redefined the concept of
> maximum frequency of a part. This means that a fraction of cores can reach
> maximum frequency. To find the best process scheduling policy for a given
> scenario, OS needs to know the core ordering informed by the platform through
> highest performance capability register of the CPPC interface.
> 
> Earlier implementations of amd-pstate preferred core only support a static
> core ranking and targeted performance. Now it has the ability to dynamically
> change the preferred core based on the workload and platform conditions and
> accounting for thermals and aging.
> 
> Amd-pstate driver utilizes the functions and data structures provided by
> the ITMT architecture to enable the scheduler to favor scheduling on cores
> which can be get a higher frequency with lower voltage.
> We call it amd-pstate preferred core.
> 
> Here sched_set_itmt_core_prio() is called to set priorities and
> sched_set_itmt_support() is called to enable ITMT feature.
> Amd-pstate driver uses the highest performance value to indicate
> the priority of CPU. The higher value has a higher priority.
> 
> Amd-pstate driver will provide an initial core ordering at boot time.
> It relies on the CPPC interface to communicate the core ranking to the
> operating system and scheduler to make sure that OS is choosing the cores
> with highest performance firstly for scheduling the process. When amd-pstate
> driver receives a message with the highest performance change, it will
> update the core ranking.
> 
> Changes form V6->V7:
> - x86:
> - - Modify kconfig about X86_AMD_PSTATE.
> - cpufreq: amd-pstate:
> - - modify incorrect comments about scheduler_work().
> - - convert highest_perf data type.
> - - modify preferred core init when cpu init and online.
> - acpi: cppc:
> - - modify link of CPPC highest performance.
> - cpufreq:
> - - modify link of CPPC highest performance changed.
> 
> Changes form V5->V6:
> - cpufreq: amd-pstate:
> - - modify the wrong tag order.
> - - modify warning about hw_prefcore sysfs attribute.
> - - delete duplicate comments.
> - - modify the variable name cppc_highest_perf to prefcore_ranking.
> - - modify judgment conditions for setting highest_perf.
> - - modify sysfs attribute for CPPC highest perf to pr_debug message.
> - Documentation: amd-pstate:
> - - modify warning: title underline too short.
> 
> Changes form V4->V5:
> - cpufreq: amd-pstate:
> - - modify sysfs attribute for CPPC highest perf.
> - - modify warning about comments
> - - rebase linux-next
> - cpufreq: 
> - - Moidfy warning about function declarations.
> - Documentation: amd-pstate:
> - - align with ``amd-pstat``
> 
> Changes form V3->V4:
> - Documentation: amd-pstate:
> - - Modify inappropriate descriptions.
> 
> Changes form V2->V3:
> - x86:
> - - Modify kconfig and description.
> - cpufreq: amd-pstate: 
> - - Add Co-developed-by tag in commit message.
> - cpufreq:
> - - Modify commit message.
> - Documentation: amd-pstate:
> - - Modify inappropriate descriptions.
> 
> Changes form V1->V2:
> - acpi: cppc:
> - - Add reference link.
> - cpufreq:
> - - Moidfy link error.
> - cpufreq: amd-pstate: 
> - - Init the priorities of all online CPUs
> - - Use a single variable to represent the status of preferred core.
> - Documentation:
> - - Default enabled preferred core.
> - Documentation: amd-pstate: 
> - - Modify inappropriate descriptions.
> - - Default enabled preferred core.
> - - Use a single variable to represent the status of preferred core.
> 
> Meng Li (7):
>   x86: Drop CPU_SUP_INTEL from SCHED_MC_PRIO for the expansion.
>   acpi: cppc: Add get the highest performance cppc control
>   cpufreq: amd-pstate: Enable amd-pstate preferred core supporting.
>   cpufreq: Add a notification message that the highest perf has changed
>   cpufreq: amd-pstate: Update amd-pstate preferred core ranking
>     dynamically
>   Documentation: amd-pstate: introduce amd-pstate preferred core
>   Documentation: introduce amd-pstate preferrd core mode kernel command
>     line options
> 
>  .../admin-guide/kernel-parameters.txt         |   5 +
>  Documentation/admin-guide/pm/amd-pstate.rst   |  58 +++++-
>  arch/x86/Kconfig                              |   5 +-
>  drivers/acpi/cppc_acpi.c                      |  13 ++
>  drivers/acpi/processor_driver.c               |   6 +
>  drivers/cpufreq/amd-pstate.c                  | 197 ++++++++++++++++--
>  drivers/cpufreq/cpufreq.c                     |  13 ++
>  include/acpi/cppc_acpi.h                      |   5 +
>  include/linux/amd-pstate.h                    |   6 +
>  include/linux/cpufreq.h                       |   5 +
>  10 files changed, 291 insertions(+), 22 deletions(-)

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?

Thanks.

-- 
Oleksandr Natalenko (post-factum)
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