linux-kernel - Re: [PATCH v8 05/10] fs/resctrl: Introduce interface to display "io

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Message-ID: <67bd0215-8380-4207-bf97-bfd1d08d7faa@amd.com>
Date: Fri, 22 Aug 2025 17:12:34 -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, manali.shukla@....com, gautham.shenoy@....com
Subject: Re: [PATCH v8 05/10] fs/resctrl: Introduce interface to display
 "io_alloc" support

Hi Reinette,

On 8/7/2025 8:48 PM, Reinette Chatre wrote:
> Hi Babu,
>
> On 8/5/25 4:30 PM, Babu Moger wrote:
>> "io_alloc" feature in resctrl allows direct insertion of data from I/O
>> devices into the cache.
>>
>> Introduce the 'io_alloc' resctrl file to indicate the support for the
>> feature.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> ...
>
>> ---
>>   Documentation/filesystems/resctrl.rst | 29 +++++++++++++++++++++++++++
>>   fs/resctrl/ctrlmondata.c              | 21 +++++++++++++++++++
>>   fs/resctrl/internal.h                 |  5 +++++
>>   fs/resctrl/rdtgroup.c                 | 24 +++++++++++++++++++++-
>>   4 files changed, 78 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>> index f08699030312..fff7e04d1e2a 100644
>> --- a/Documentation/filesystems/resctrl.rst
>> +++ b/Documentation/filesystems/resctrl.rst
>> @@ -136,6 +136,35 @@ related to allocation:
>>   			"1":
>>   			      Non-contiguous 1s value in CBM is supported.
>>   
>> +"io_alloc":
>> +		"io_alloc" enables system software to configure the portion of
>> +		the cache allocated for I/O traffic. File may only exist if the
>> +		system supports this feature on some of its cache resources.
>> +
>> +			"disabled":
>> +			      Portions of cache used for allocation of I/O traffic
>> +			      cannot be configured.
> To help distinguish difference between "disabled" and "not supported" it may be useful
> to prepend something like "Resource supports "io_alloc" but the feature is disabled."


Sure. Added it now.

>
>> +			"enabled":
>> +			      Portions of cache used for allocation of I/O traffic
>> +			      can be configured using "io_alloc_cbm".
>> +			"not supported":
>> +			      Support not available for this resource.
>> +
>> +		The underlying implementation may reduce resources available to
>> +		general (CPU) cache allocation. See architecture specific notes
>> +		below. Depending on usage requirements the feature can be enabled
>> +		or disabled.
>> +
>> +		On AMD systems, the io_alloc feature is supported by the L3 Smart
> drop "the"?


Sure.

>
>> +		Data Cache Injection Allocation Enforcement (SDCIAE). The CLOSID for
>> +		io_alloc is the highest CLOSID supported by the resource. When
>> +		io_alloc is enabled, the highest CLOSID is dedicated to io_alloc and
>> +		no longer available for general (CPU) cache allocation. When CDP is
>> +		enabled, io_alloc routes I/O traffic using the highest CLOSID allocated
>> +		for the instruction cache (L3CODE), making this CLOSID no longer
>> +		available for general (CPU) cache allocation for both the L3CODE and
>> +		L3DATA resources.
>> +
>>   Memory bandwidth(MB) subdirectory contains the following files
>>   with respect to allocation:
>>   
> Code looks good to me.
>
Thanks

Babu

>
>