linux-kernel - Re: [PATCH] cpufreq/amd-pstate: Refactor max frequency calculation

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Message-ID: <b1210cbf-22c8-48f1-ad50-d81395abc8f3@amd.com>
Date: Wed, 18 Dec 2024 13:20:09 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: Naresh Solanki <naresh.solanki@...ements.com>
Cc: Huang Rui <ray.huang@....com>, "Gautham R. Shenoy"
 <gautham.shenoy@....com>, Perry Yuan <perry.yuan@....com>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq/amd-pstate: Refactor max frequency calculation

On 12/18/2024 13:00, Naresh Solanki wrote:
> Refactor to calculate max-freq more accurately.

Can you add some more detail about what you're finding?
What was it before, what is it now, why is it more accurate?

> 
> Signed-off-by: Naresh Solanki <naresh.solanki@...ements.com>
> ---
>   drivers/cpufreq/amd-pstate.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index d7630bab2516..78a2cbd14952 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -892,7 +892,7 @@ static int amd_pstate_init_freq(struct amd_cpudata *cpudata)
>   	u64 numerator;
>   	u32 nominal_perf, nominal_freq;
>   	u32 lowest_nonlinear_perf, lowest_nonlinear_freq;
> -	u32 boost_ratio, lowest_nonlinear_ratio;
> +	u32 lowest_nonlinear_ratio;
>   	struct cppc_perf_caps cppc_perf;
>   
>   	ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
> @@ -914,8 +914,7 @@ static int amd_pstate_init_freq(struct amd_cpudata *cpudata)
>   	ret = amd_get_boost_ratio_numerator(cpudata->cpu, &numerator);
>   	if (ret)
>   		return ret;
> -	boost_ratio = div_u64(numerator << SCHED_CAPACITY_SHIFT, nominal_perf);
> -	max_freq = (nominal_freq * boost_ratio >> SCHED_CAPACITY_SHIFT) * 1000;
> +	max_freq = div_u64(numerator * nominal_freq * 1000, nominal_perf);

This doesn't apply currently, because of some changes in the 
superm1.git/linux-next branch; specifically:

https://git.kernel.org/superm1/c/68cb0e77b6439

I haven't sent this out to linux-pm yet so it could be in linux-next, 
but will be doing that soon.  So can you please rebase on that branch if 
this change still makes sense?

>   
>   	lowest_nonlinear_perf = READ_ONCE(cpudata->lowest_nonlinear_perf);
>   	lowest_nonlinear_ratio = div_u64(lowest_nonlinear_perf << SCHED_CAPACITY_SHIFT,