linux-kernel - Re: [PATCH v3 10/15] cpufreq/amd-pstate: Move limit updating code

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Message-ID: <d120814f-7393-4d10-a6de-ba09948f4243@amd.com>
Date: Mon, 16 Dec 2024 19:46:36 +0530
From: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>
To: Mario Limonciello <mario.limonciello@....com>,
 "Gautham R . Shenoy" <gautham.shenoy@....com>
Cc: Perry Yuan <perry.yuan@....com>, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 10/15] cpufreq/amd-pstate: Move limit updating code

Hello Mario,

On 12/10/2024 12:22 AM, Mario Limonciello wrote:
> The limit updating code in amd_pstate_epp_update_limit() should not
> only apply to EPP updates.  Move it to amd_pstate_update_min_max_limit()
> so other callers can benefit as well.
> 
> With this move it's not necessary to have clamp_t calls anymore because
> the verify callback is called when setting limits.

While testing this series, I observed that with amd_pstate=passive + schedutil governor,
the scaling_max_freq limits were not being honored and I bisected the issue down to this 
patch.

I went through the code and noticed that in amd_pstate_adjust_perf(), we set the min_perf 
field in MSR_AMD_CPPC_REQ to "cap_perf" which is equal to cpudata->highest_perf (which is 
equal to 255 for non-preferred cores systems). This didnt seem logical to me and I changed 
cap_perf to cpudata->max_limit_perf which gives us the value updated in scaling_max_freq. 

I think as we removed the redundant clamping code, this pre-existing issue got exposed. 
The below diff fixes the issue for me. 

Please let me know your thoughts on this.

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index d7b1de97727a..1ac34e3f1fc5 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -699,7 +699,7 @@ static void amd_pstate_adjust_perf(unsigned int cpu,
        if (min_perf < lowest_nonlinear_perf)
                min_perf = lowest_nonlinear_perf;

-       max_perf = cap_perf;
+       max_perf = cpudata->max_limit_perf;
        if (max_perf < min_perf)
                max_perf = min_perf;

Thanks,
Dhananjay

> 
> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
> v2:
>  * Drop lowest_perf variable
> ---
>  drivers/cpufreq/amd-pstate.c | 28 +++++-----------------------
>  1 file changed, 5 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 3a3df67c096d5..dc3c45b6f5103 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -537,10 +537,6 @@ static void amd_pstate_update(struct amd_cpudata *cpudata, u32 min_perf,
>  	u32 nominal_perf = READ_ONCE(cpudata->nominal_perf);
>  	u64 value = prev;
>  
> -	min_perf = clamp_t(unsigned long, min_perf, cpudata->min_limit_perf,
> -			cpudata->max_limit_perf);
> -	max_perf = clamp_t(unsigned long, max_perf, cpudata->min_limit_perf,
> -			cpudata->max_limit_perf);
>  	des_perf = clamp_t(unsigned long, des_perf, min_perf, max_perf);
>  
>  	max_freq = READ_ONCE(cpudata->max_limit_freq);
> @@ -607,7 +603,7 @@ static int amd_pstate_verify(struct cpufreq_policy_data *policy_data)
>  
>  static int amd_pstate_update_min_max_limit(struct cpufreq_policy *policy)
>  {
> -	u32 max_limit_perf, min_limit_perf, lowest_perf, max_perf, max_freq;
> +	u32 max_limit_perf, min_limit_perf, max_perf, max_freq;
>  	struct amd_cpudata *cpudata = policy->driver_data;
>  
>  	max_perf = READ_ONCE(cpudata->highest_perf);
> @@ -615,12 +611,8 @@ static int amd_pstate_update_min_max_limit(struct cpufreq_policy *policy)
>  	max_limit_perf = div_u64(policy->max * max_perf, max_freq);
>  	min_limit_perf = div_u64(policy->min * max_perf, max_freq);
>  
> -	lowest_perf = READ_ONCE(cpudata->lowest_perf);
> -	if (min_limit_perf < lowest_perf)
> -		min_limit_perf = lowest_perf;
> -
> -	if (max_limit_perf < min_limit_perf)
> -		max_limit_perf = min_limit_perf;
> +	if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
> +		min_limit_perf = min(cpudata->nominal_perf, max_limit_perf);
>  
>  	WRITE_ONCE(cpudata->max_limit_perf, max_limit_perf);
>  	WRITE_ONCE(cpudata->min_limit_perf, min_limit_perf);
> @@ -1562,28 +1554,18 @@ static void amd_pstate_epp_cpu_exit(struct cpufreq_policy *policy)
>  static int amd_pstate_epp_update_limit(struct cpufreq_policy *policy)
>  {
>  	struct amd_cpudata *cpudata = policy->driver_data;
> -	u32 max_perf, min_perf;
>  	u64 value;
>  	s16 epp;
>  
> -	max_perf = READ_ONCE(cpudata->highest_perf);
> -	min_perf = READ_ONCE(cpudata->lowest_perf);
>  	amd_pstate_update_min_max_limit(policy);
>  
> -	max_perf = clamp_t(unsigned long, max_perf, cpudata->min_limit_perf,
> -			cpudata->max_limit_perf);
> -	min_perf = clamp_t(unsigned long, min_perf, cpudata->min_limit_perf,
> -			cpudata->max_limit_perf);
>  	value = READ_ONCE(cpudata->cppc_req_cached);
>  
> -	if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
> -		min_perf = min(cpudata->nominal_perf, max_perf);
> -
>  	value &= ~(AMD_CPPC_MAX_PERF_MASK | AMD_CPPC_MIN_PERF_MASK |
>  		   AMD_CPPC_DES_PERF_MASK);
> -	value |= FIELD_PREP(AMD_CPPC_MAX_PERF_MASK, max_perf);
> +	value |= FIELD_PREP(AMD_CPPC_MAX_PERF_MASK, cpudata->max_limit_perf);
>  	value |= FIELD_PREP(AMD_CPPC_DES_PERF_MASK, 0);
> -	value |= FIELD_PREP(AMD_CPPC_MIN_PERF_MASK, min_perf);
> +	value |= FIELD_PREP(AMD_CPPC_MIN_PERF_MASK, cpudata->min_limit_perf);
>  
>  	/* Get BIOS pre-defined epp value */
>  	epp = amd_pstate_get_epp(cpudata, value);