linux-kernel - Re: [PATCH v3 1/2] x86/cpufeatures: Add AMD FAST CPPC feature flag

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Date: Mon, 27 May 2024 22:36:57 +0800
From: Xiaojian Du <xiaojidu@....com>
To: Dave Hansen <dave.hansen@...el.com>, Xiaojian Du <Xiaojian.Du@....com>,
 linux-kernel@...r.kernel.org, x86@...nel.org, linux-pm@...r.kernel.org
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, daniel.sneddon@...ux.intel.com,
 jpoimboe@...nel.org, pawan.kumar.gupta@...ux.intel.com,
 sandipan.das@....com, kai.huang@...el.com, ray.huang@....com,
 rafael@...nel.org, Perry.Yuan@....com, gautham.shenoy@....com,
 Borislav.Petkov@....com, mario.limonciello@....com
Subject: Re: [PATCH v3 1/2] x86/cpufeatures: Add AMD FAST CPPC feature flag

Thanks Dave.

Because "CPPC" has existed in the "cpufeatures.h", thinking it will add 
duplicated line so I don't expand it.
Making this new flag hidden is to avoid causing user confusion about two 
"CPPC" flags.
This new feature flag is added to choose code branch, if not, it has to 
choose a ugly way and use CPU model ID.

Thanks,
Xiaojian


On 2024/5/24 0:31, Dave Hansen wrote:
> On 5/22/24 23:16, Xiaojian Du wrote:
>>   #define X86_FEATURE_BHI_CTRL		(21*32+ 2) /* "" BHI_DIS_S HW control available */
>>   #define X86_FEATURE_CLEAR_BHB_HW	(21*32+ 3) /* "" BHI_DIS_S HW control enabled */
>>   #define X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT (21*32+ 4) /* "" Clear branch history at vmexit using SW loop */
>> +#define X86_FEATURE_FAST_CPPC		(21*32 + 5) /* "" AMD Fast CPPC */
> It'd be nice to expand the CPPC acronym at least _once_.
>
> Also, this is used _once_ at boot and not exposed in /proc/cpuinfo.  Is
> it even worth defining an X86_FEATURE_ for it?