linux-kernel - Re: [PATCH v3 07/21] cpufreq: amd: add fast switch function for amd-pstate

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Date:   Tue, 2 Nov 2021 14:56:34 -0500
From:   Nathan Fontenot <nafonten@....com>
To:     Huang Rui <ray.huang@....com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        linux-pm@...r.kernel.org
Cc:     Deepak Sharma <deepak.sharma@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Steven Noonan <steven@...vesoftware.com>,
        Nathan Fontenot <nathan.fontenot@....com>,
        Jinzhou Su <Jinzhou.Su@....com>,
        Xiaojian Du <Xiaojian.Du@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v3 07/21] cpufreq: amd: add fast switch function for
 amd-pstate

On 10/29/21 8:02 AM, Huang Rui wrote:
> Introduce the fast switch function for amd-pstate on the AMD processors
> which support the full MSR register control. It's able to decrease the
> lattency on interrupt context.
> 
> Signed-off-by: Huang Rui <ray.huang@....com>
> ---
>  drivers/cpufreq/amd-pstate.c | 38 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index a400861c7fdc..55ff03f85608 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -191,6 +191,41 @@ static int amd_pstate_target(struct cpufreq_policy *policy,
>  	return 0;
>  }
>  
> +static void amd_pstate_adjust_perf(unsigned int cpu,
> +				   unsigned long min_perf,
> +				   unsigned long target_perf,
> +				   unsigned long capacity)
> +{
> +	unsigned long amd_max_perf, amd_min_perf, amd_des_perf,
> +		      amd_cap_perf, lowest_nonlinear_perf;

You could drop the amd_ prefix to these local variables.

-Nathan

> +	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
> +	struct amd_cpudata *cpudata = policy->driver_data;
> +
> +	amd_cap_perf = READ_ONCE(cpudata->highest_perf);
> +	lowest_nonlinear_perf = READ_ONCE(cpudata->lowest_nonlinear_perf);
> +
> +	if (target_perf < capacity)
> +		amd_des_perf = DIV_ROUND_UP(amd_cap_perf * target_perf,
> +					    capacity);
> +
> +	amd_min_perf = READ_ONCE(cpudata->highest_perf);
> +	if (min_perf < capacity)
> +		amd_min_perf = DIV_ROUND_UP(amd_cap_perf * min_perf, capacity);
> +
> +	if (amd_min_perf < lowest_nonlinear_perf)
> +		amd_min_perf = lowest_nonlinear_perf;
> +
> +	amd_max_perf = amd_cap_perf;
> +	if (amd_max_perf < amd_min_perf)
> +		amd_max_perf = amd_min_perf;
> +
> +	amd_des_perf = clamp_t(unsigned long, amd_des_perf,
> +			       amd_min_perf, amd_max_perf);
> +
> +	amd_pstate_update(cpudata, amd_min_perf, amd_des_perf,
> +			  amd_max_perf, true);
> +}
> +
>  static int amd_get_min_freq(struct amd_cpudata *cpudata)
>  {
>  	struct cppc_perf_caps cppc_perf;
> @@ -311,6 +346,8 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>  	/* It will be updated by governor */
>  	policy->cur = policy->cpuinfo.min_freq;
>  
> +	policy->fast_switch_possible = true;
> +
>  	ret = freq_qos_add_request(&policy->constraints, &cpudata->req[0],
>  				   FREQ_QOS_MIN, policy->cpuinfo.min_freq);
>  	if (ret < 0) {
> @@ -360,6 +397,7 @@ static struct cpufreq_driver amd_pstate_driver = {
>  	.flags		= CPUFREQ_CONST_LOOPS | CPUFREQ_NEED_UPDATE_LIMITS,
>  	.verify		= amd_pstate_verify,
>  	.target		= amd_pstate_target,
> +	.adjust_perf    = amd_pstate_adjust_perf,
>  	.init		= amd_pstate_cpu_init,
>  	.exit		= amd_pstate_cpu_exit,
>  	.name		= "amd-pstate",
>