linux-kernel - Re: [PATCH 4/5] Documentation: amd-pstate: add driver working mode introduction

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Message-ID: <Y3W1eGfSQBsCASUG@BLR-5CG11610CF.amd.com>
Date:   Thu, 17 Nov 2022 09:45:52 +0530
From:   "Gautham R. Shenoy" <gautham.shenoy@....com>
To:     Perry Yuan <Perry.Yuan@....com>
Cc:     rafael.j.wysocki@...el.com, ray.huang@....com,
        viresh.kumar@...aro.org, Mario.Limonciello@....com,
        Nathan.Fontenot@....com, Alexander.Deucher@....com,
        Deepak.Sharma@....com, Shimmer.Huang@....com, Li.Meng@....com,
        Xiaojian.Du@....com, wyes.karny@....com, ananth.narayan@....com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] Documentation: amd-pstate: add driver working mode
 introduction

Hello Perry,

On Thu, Nov 17, 2022 at 10:49:54AM +0800, Perry Yuan wrote:
> Introduce the `amd-pstate` driver new working mode with
> `amd-pstate=passive` added to kernel command line.

It should be `amd_pstate=passive` here to be consistent with the early
parameter and the rest of the documentation.


> If there is no passive mode enabled by user, amd-pstate driver will be
> disabled by default for now.
> 
> Signed-off-by: Perry Yuan <Perry.Yuan@....com>
> ---
>  Documentation/admin-guide/pm/amd-pstate.rst | 30 +++++++++------------
>  1 file changed, 13 insertions(+), 17 deletions(-)
> 
> diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
> index 8f3d30c5a0d8..06e23538f79c 100644
> --- a/Documentation/admin-guide/pm/amd-pstate.rst
> +++ b/Documentation/admin-guide/pm/amd-pstate.rst
> @@ -283,23 +283,19 @@ efficiency frequency management method on AMD processors.
>  Kernel Module Options for ``amd-pstate``
>  =========================================
>  
> -.. _shared_mem:
> -
> -``shared_mem``
> -Use a module param (shared_mem) to enable related processors manually with
> -**amd_pstate.shared_mem=1**.
> -Due to the performance issue on the processors with `Shared Memory Support
> -<perf_cap_>`_, we disable it presently and will re-enable this by default
> -once we address performance issue with this solution.
> -
> -To check whether the current processor is using `Full MSR Support <perf_cap_>`_
> -or `Shared Memory Support <perf_cap_>`_ : ::
> -
> -  ray@...test1:~$ lscpu | grep cppc
> -  Flags:                           fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 x2apic movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb cat_l3 cdp_l3 hw_pstate ssbd mba ibrs ibpb stibp vmmcall fsgsbase bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a rdseed adx smap clflushopt clwb sha_ni xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local clzero irperf xsaveerptr rdpru wbnoinvd cppc arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif v_spec_ctrl umip pku ospke vaes vpclmulqdq rdpid overflow_recov succor smca fsrm
> -
> -If the CPU flags have ``cppc``, then this processor supports `Full MSR Support
> -<perf_cap_>`_. Otherwise, it supports `Shared Memory Support <perf_cap_>`_.
> +Passive Mode
> +------------
> +
> +``amd_pstate=passive``
> +
> +It will be enabled if the ``amd_pstate=passive`` is passed to the kernel in the command line.
> +In this mode, ``amd_pstate`` driver software specifies a desired QoS target in the CPPC
> +performance scale as a relative number. This can be expressed as percentage of nominal
> +performance (infrastructure max). Below the nominal sustained performance level,
> +desired performance expresses the average performance level of the processor subject
> +to the Performance Reduction Tolerance register. Above the nominal performance level,
> +processor must provide at least nominal performance requested and go higher if current
> +operating conditions allow.

Otherwise looks good to me.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>

--
Thanks and Regards
gautham.