linux-kernel - Re: [PATCH 8/8] cpufreq: amd-pstate: Drop some uses of cpudata->hw

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Message-ID: <61b96549-2969-4b64-a40d-f91f614ec3ab@amd.com>
Date: Tue, 27 Aug 2024 14:16:51 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: "Gautham R. Shenoy" <gautham.shenoy@....com>,
 Mario Limonciello <superm1@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>, Perry Yuan <perry.yuan@....com>,
 "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
 "Rafael J . Wysocki" <rafael@...nel.org>,
 "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
 <linux-kernel@...r.kernel.org>, "open list:ACPI"
 <linux-acpi@...r.kernel.org>,
 "open list:CPU FREQUENCY SCALING FRAMEWORK" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 8/8] cpufreq: amd-pstate: Drop some uses of
 cpudata->hw_prefcore

On 8/27/2024 12:03, Gautham R. Shenoy wrote:
> On Mon, Aug 26, 2024 at 04:13:58PM -0500, Mario Limonciello wrote:
>> From: Mario Limonciello <mario.limonciello@....com>
>>
>> As the global variable is cleared when preferred cores is not present
>> the local variable use isn't needed in many functions.
>> Drop it where possible.  No intended functional changes.
>>
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>> ---
>>   drivers/cpufreq/amd-pstate.c | 7 +------
>>   1 file changed, 1 insertion(+), 6 deletions(-)
>>
>> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
>> index ed05d7a0add10..257e28e549bd1 100644
>> --- a/drivers/cpufreq/amd-pstate.c
>> +++ b/drivers/cpufreq/amd-pstate.c
>> @@ -1112,12 +1112,7 @@ static ssize_t show_amd_pstate_prefcore_ranking(struct cpufreq_policy *policy,
>>   static ssize_t show_amd_pstate_hw_prefcore(struct cpufreq_policy *policy,
>>   					   char *buf)
>>   {
>> -	bool hw_prefcore;
>> -	struct amd_cpudata *cpudata = policy->driver_data;
>> -
>> -	hw_prefcore = READ_ONCE(cpudata->hw_prefcore);
>> -
>> -	return sysfs_emit(buf, "%s\n", str_enabled_disabled(hw_prefcore));
>> +	return sysfs_emit(buf, "%s\n", str_enabled_disabled(amd_pstate_prefcore));
> 
> 
> If the user boots with "amd_prefcore=disable" on a system that
> supports preferred-core, pror to this patchset, cpudata->hw_prefcore
> would be true and thus, amd_pstate_hw_prefcore would show "enabled".
> 

Yes; you're right about the previous behavior.

> With this patchset, it would show "disabled". Or am I missing something?

This appears to be another case we don't have documentation for the 
sysfs file `amd_pstate_hw_prefcore`.

I had thought this was a malfunction in the behavior that it reflected 
the current status, not the hardware /capability/.

Which one makes more sense for userspace?  In my mind the most likely 
consumer of this information would be something a sched_ext based 
userspace scheduler.  They would need to know whether the scheduler was 
using preferred cores; not whether the hardware supported it.

Whichever direction we agree to go; I'll add documentation for v2.

> 
> 
> 
>>   }
>>   
>>   static ssize_t show_energy_performance_available_preferences(
>> -- 
>> 2.43.0
>>
> 
> --
> Thanks and Regards
> gautham.