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

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Date: Wed, 1 May 2024 10:14:47 -0700
From: Vanshidhar Konda <vanshikonda@...amperecomputing.com>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: liwei <liwei728@...wei.com>, Ionela Voinescu <ionela.voinescu@....com>, 
	Beata Michalska <beata.michalska@....com>, 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: Re: [PATCH] cpufreq/cppc: changing highest_perf to nominal_perf
 in cppc_cpufreq_cpu_init()

On Mon, Apr 29, 2024 at 04:19:45PM +0530, Viresh Kumar wrote:
>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;
>>

This seems like the safer thing to do.

Reviewed-by: Vanshidhar Konda <vanshikonda@...amperecomputing.com>

>>  	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