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

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Message-ID: <a92eb6e2-1636-4f80-8db9-23bbcf885337@amd.com>
Date: Wed, 21 Feb 2024 12:47:43 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: Lucas Lee Jing Yi <lucasleeeeeeeee@...il.com>, oleksandr@...alenko.name
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,
 nathan.fontenot@....com, rafael.j.wysocki@...el.com, rafael@...nel.org,
 ray.huang@....com, shimmer.huang@....com, skhan@...uxfoundation.org,
 viresh.kumar@...aro.org, x86@...nel.org
Subject: Re: [PATCH] [PATCH] amd_pstate: fix erroneous highest_perf value on
 some CPUs

On 2/21/2024 11:19, 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
> 

Yes; the max boost for your system should be 5.1GHz according to the 
specification [1].

Would you please open a kernel Bugzilla and attach an acpidump and dmesg 
for your system?  I believe we need to better understand your system's 
situation before deciding on how to correctly approach it.

[1] https://www.amd.com/en/product/13041

> 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);