linux-kernel - Re: [PATCH] [PATCH] amd_pstate: fix erroneous highest

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Message-ID: <3868832.mvXUDI8C0e@natalenko.name>
Date: Tue, 20 Feb 2024 10:02:48 +0100
From: Oleksandr Natalenko <oleksandr@...alenko.name>
To: rafael@...nel.org, Lucas Lee Jing Yi <lucasleeeeeeeee@...il.com>
Cc: Perry.Yuan@....com, Xiaojian.Du@....com, alexander.deucher@....com,
 bp@...en8.de, deepak.sharma@....com, li.meng@....com,
 linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, linux-pm@...r.kernel.org,
 mario.limonciello@....com, nathan.fontenot@....com,
 rafael.j.wysocki@...el.com, ray.huang@....com, shimmer.huang@....com,
 skhan@...uxfoundation.org, viresh.kumar@...aro.org, x86@...nel.org,
 Lucas Lee Jing Yi <lucasleeeeeeeee@...il.com>
Subject:
 Re: [PATCH] [PATCH] amd_pstate: fix erroneous highest_perf value on some CPUs

Hello.

On neděle 18. února 2024 17:10:31 CET Lucas Lee Jing Yi wrote:
> On a Ryzen 7840HS the highest_perf value is 196, not 166 as AMD assumed.
> This leads to the advertised max clock speed to only be 4.35ghz instead of 5.14ghz , leading to a large degradation in performance.
> 
> Fix the broken assumption and revert back to the old logic for getting highest_perf.
> 
> TEST:
> Geekbench 6 Before Patch:
> Single Core:	2325 (-22%)!
> Multi Core:	11335 (-10%)
> 
> Geekbench 6 AFTER Patch:
> Single Core:	2635
> Multi Core:	12487
> 
> Signed-off-by: Lucas Lee Jing Yi <lucasleeeeeeeee@...il.com>
> ---
>  drivers/cpufreq/amd-pstate.c | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 08e112444c27..54df68773620 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -50,7 +50,6 @@
>  
>  #define AMD_PSTATE_TRANSITION_LATENCY	20000
>  #define AMD_PSTATE_TRANSITION_DELAY	1000
> -#define AMD_PSTATE_PREFCORE_THRESHOLD	166
>  
>  /*
>   * TODO: We need more time to fine tune processors with shared memory solution
> @@ -299,15 +298,12 @@ static int pstate_init_perf(struct amd_cpudata *cpudata)
>  				     &cap1);
>  	if (ret)
>  		return ret;
> -
> -	/* For platforms that do not support the preferred core feature, the
> -	 * highest_pef may be configured with 166 or 255, to avoid max frequency
> -	 * calculated wrongly. we take the AMD_CPPC_HIGHEST_PERF(cap1) value as
> -	 * the default max perf.
> + 
> +	/* Some CPUs have different highest_perf from others, it is safer 
> +	 * to read it than to assume some erroneous value, leading to performance issues.
>  	 */
> -	if (cpudata->hw_prefcore)
> -		highest_perf = AMD_PSTATE_PREFCORE_THRESHOLD;
> -	else
> +	highest_perf = amd_get_highest_perf();
> +	if(highest_perf > AMD_CPPC_HIGHEST_PERF(cap1))
>  		highest_perf = AMD_CPPC_HIGHEST_PERF(cap1);
>  
>  	WRITE_ONCE(cpudata->highest_perf, highest_perf);
> @@ -329,9 +325,11 @@ static int cppc_init_perf(struct amd_cpudata *cpudata)
>  	if (ret)
>  		return ret;
>  
> -	if (cpudata->hw_prefcore)
> -		highest_perf = AMD_PSTATE_PREFCORE_THRESHOLD;
> -	else
> +	/* Some CPUs have different highest_perf from others, it is safer 
> +	 * to read it than to assume some erroneous value, leading to performance issues.
> +	 */
> +	highest_perf = amd_get_highest_perf();
> +	if(highest_perf > cppc_perf.highest_perf)
>  		highest_perf = cppc_perf.highest_perf;
>  
>  	WRITE_ONCE(cpudata->highest_perf, highest_perf);
> 

Please pay attention to trailing whitespaces, adding whitespaces to blank lines, and whitespaces between `if` and opening `(`.

`scripts/checkpatch.pl` may help you with that.

Thank you.

-- 
Oleksandr Natalenko (post-factum)
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