linux-kernel - Re: [PATCH] cpufreq/cppc: changing highest_perf to nominal_perf in cppc_cpufreq_cpu

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Date: Mon, 29 Apr 2024 16:19:45 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: liwei <liwei728@...wei.com>, Ionela Voinescu <ionela.voinescu@....com>,
	Beata Michalska <beata.michalska@....com>,
	Vanshidhar Konda <vanshikonda@...amperecomputing.com>
Cc: rafael@...nel.org, al.stone@...aro.org, ashwin.chaugule@...aro.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	liwei391@...wei.com, liaoyu15@...wei.com
Subject: Re: [PATCH] cpufreq/cppc: changing highest_perf to nominal_perf in
 cppc_cpufreq_cpu_init()

CC'ing few folks who are working with the driver.

On 28-04-24, 17:28, liwei wrote:
> When turning on turbo, if frequency configuration takes effect slowly,
> the updated policy->cur may be equal to the frequency configured in
> governor->limits(), performance governor will not adjust the frequency,
> configured frequency will remain at turbo-freq.
> 
> Simplified call stack looks as follows:
> cpufreq_register_driver(&cppc_cpufreq_driver)
> 	...
> 	cppc_cpufreq_cpu_init()
> 		cppc_get_perf_caps()
> 		policy->max = cppc_perf_to_khz(caps, caps->nominal_perf)
> 			cppc_set_perf(highest_perf) // set highest_perf
> 			policy->cur = cpufreq_driver->get() // if cur == policy->max
> 	cpufreq_init_policy()
> 		...
> 		cpufreq_start_governor() // governor: performance
> 			new_freq = cpufreq_driver->get() // if new_freq == policy->max
> 			if (policy->cur != new_freq)
> 			cpufreq_out_of_sync(policy, new_freq)
> 				...
> 				policy->cur = new_freq
> 			...
> 			policy->governor->limits()
> 				__cpufreq_driver_target(policy->max)
> 					if (policy->cur==target)
> 					// generate error, keep set highest_perf
> 						ret
> 					cppc_set_perf(target)
> 
> Fix this by changing highest_perf to nominal_perf in cppc_cpufreq_cpu_init().
> 
> Fixes: 5477fb3bd1e8 ("ACPI / CPPC: Add a CPUFreq driver for use with CPPC")
> Signed-off-by: liwei <liwei728@...wei.com>
> ---
>  drivers/cpufreq/cppc_cpufreq.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 64420d9cfd1e..db04a82b8a97 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -669,14 +669,14 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  	if (caps->highest_perf > caps->nominal_perf)
>  		boost_supported = true;
>  
> -	/* Set policy->cur to max now. The governors will adjust later. */
> -	policy->cur = cppc_perf_to_khz(caps, caps->highest_perf);
> -	cpu_data->perf_ctrls.desired_perf =  caps->highest_perf;
> +	/* Set policy->cur to norm now. */
> +	policy->cur = cppc_perf_to_khz(caps, caps->nominal_perf);
> +	cpu_data->perf_ctrls.desired_perf =  caps->nominal_perf;
>  
>  	ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
>  	if (ret) {
>  		pr_debug("Err setting perf value:%d on CPU:%d. ret:%d\n",
> -			 caps->highest_perf, cpu, ret);
> +			 caps->nominal_perf, cpu, ret);
>  		goto out;
>  	}
>  
> -- 
> 2.25.1

-- 
viresh