linux-kernel - Re: [PATCH v5 6/7] cpufreq: amd-pstate: update pstate frequency transition delay time

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Message-ID: <87bkslim2c.fsf@stealth>
Date:   Mon, 15 Aug 2022 16:05:47 +0100
From:   Punit Agrawal <punit.agrawal@...edance.com>
To:     Perry Yuan <Perry.Yuan@....com>
Cc:     <rafael.j.wysocki@...el.com>, <ray.huang@....com>,
        <viresh.kumar@...aro.org>, <Deepak.Sharma@....com>,
        <Mario.Limonciello@....com>, <Nathan.Fontenot@....com>,
        <Alexander.Deucher@....com>, <Jinzhou.Su@....com>,
        <Shimmer.Huang@....com>, <Xiaojian.Du@....com>, <Li.Meng@....com>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 6/7] cpufreq: amd-pstate: update pstate frequency
 transition delay time

Perry Yuan <Perry.Yuan@....com> writes:

> Change the default transition latency to be 20ms that is more
> reasonable transition delay for AMD processors in non-EPP driver mode.
>
> Update transition delay time to 1ms, in the AMD CPU autonomous mode and
> non-autonomous mode, CPPC firmware will decide frequency at 1ms timescale
> based on the workload utilization.
>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Perry Yuan <Perry.Yuan@....com>
> ---
>  drivers/cpufreq/amd-pstate.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index e40177d14310..9cb051d61422 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -41,8 +41,8 @@
>  #include <asm/msr.h>
>  #include "amd-pstate-trace.h"
>  
> -#define AMD_PSTATE_TRANSITION_LATENCY	0x20000
> -#define AMD_PSTATE_TRANSITION_DELAY	500
> +#define AMD_PSTATE_TRANSITION_LATENCY	20000
> +#define AMD_PSTATE_TRANSITION_DELAY	1000

How were these values derived? If from documentation, it'll be good to
add a link to the relevant documentation. And if they were derived from
testing, please mention this in the commit log (along with some details
of the tests used to determine the value).

>  
>  /*
>   * TODO: We need more time to fine tune processors with shared memory solution