linux-kernel - Re: [PATCH v7 04/10] x86,fs/resctrl: Implement "io

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Message-ID: <4abaacdc-4b13-4752-a0c6-e55c428e91f2@amd.com>
Date: Thu, 31 Jul 2025 12:40:02 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 tony.luck@...el.com, Dave.Martin@....com, james.morse@....com,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, akpm@...ux-foundation.org,
 paulmck@...nel.org, rostedt@...dmis.org, Neeraj.Upadhyay@....com,
 david@...hat.com, arnd@...db.de, fvdl@...gle.com, seanjc@...gle.com,
 thomas.lendacky@....com, pawan.kumar.gupta@...ux.intel.com,
 yosry.ahmed@...ux.dev, sohil.mehta@...el.com, xin@...or.com,
 kai.huang@...el.com, xiaoyao.li@...el.com, peterz@...radead.org,
 me@...aill.net, mario.limonciello@....com, xin3.li@...el.com,
 ebiggers@...gle.com, ak@...ux.intel.com, chang.seok.bae@...el.com,
 andrew.cooper3@...rix.com, perry.yuan@....com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 04/10] x86,fs/resctrl: Implement "io_alloc"
 enable/disable handlers



On 7/21/25 18:32, Reinette Chatre wrote:
> Hi Babu,
> 
> On 7/10/25 10:16 AM, Babu Moger wrote:
>> "io_alloc" enables direct insertion of data from I/O devices into the
>> cache.
>>
>> On AMD systems, "io_alloc" feature is backed by L3 Smart Data Cache
>> Injection Allocation Enforcement (SDCIAE). Change SDCIAE state by setting
>> (to enable) or clearing (to disable) bit 1 of MSR L3_QOS_EXT_CFG on all
>> logical processors within the cache domain.
>>
>> Introduce architecture-specific call to enable and disable the feature.
>>
>> The SDCIAE feature details are available in APM listed below [1].
>> [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming
>> Publication # 24593 Revision 3.41 section 19.4.7 L3 Smart Data Cache
>> Injection Allocation Enforcement (SDCIAE)
>>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> 
> ...
> 
>>  
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 885026468440..c165ac333336 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> 
> The code looks good to me but rdtgroup.c is becoming bloated by being the default place for
> any resctrl changes. While I do know there are counter examples (and I admit I do
> not have a clear understanding of original intent) ctrlmondata.c is documented and supported
> by its content as the place for cache allocation code. Could you please move these changes
> to arch/x86/kernel/cpu/resctrl/ctrlmondata.c? I will try to highlight the other places where
> I believe the either fs/resctrl/ctrlmondata.c or arch/x86/kernel/cpu/resctrl/ctrlmondata.c is
> more appropriate but please as a high level consider where appropriate to move the IO alloc
> code to be with the rest of the cache allocation code. Looking at the series it will help keep
> a couple of existing static functions static and keep data structures local to cache allocation
> code.
> 

Sure. Moved it to arch/x86/kernel/cpu/resctrl/ctrlmondata.c.
-- 
Thanks
Babu Moger