linux-kernel - Re: [PATCH v9 05/10] fs/resctrl: Introduce interface to display "io

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Message-ID: <c6102b72-3458-41c6-8650-7e70b175cc2a@amd.com>
Date: Fri, 19 Sep 2025 12:49:33 -0500
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 Babu Moger <babu.moger@....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, kas@...nel.org,
 rick.p.edgecombe@...el.com, akpm@...ux-foundation.org, paulmck@...nel.org,
 pmladek@...e.com, pawan.kumar.gupta@...ux.intel.com, rostedt@...dmis.org,
 kees@...nel.org, arnd@...db.de, fvdl@...gle.com, seanjc@...gle.com,
 thomas.lendacky@....com, manali.shukla@....com, perry.yuan@....com,
 sohil.mehta@...el.com, xin@...or.com, peterz@...radead.org,
 mario.limonciello@....com, gautham.shenoy@....com, nikunj@....com,
 dapeng1.mi@...ux.intel.com, ak@...ux.intel.com, chang.seok.bae@...el.com,
 ebiggers@...gle.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev, kvm@...r.kernel.org
Subject: Re: [PATCH v9 05/10] fs/resctrl: Introduce interface to display
 "io_alloc" support

Hi Reinette,

On 9/18/2025 12:28 AM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 9/2/25 3:41 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.
> 
> Changelog that aims to address feeback received in ABMC series (avoid repetition
> and document any non-obvious things), please feel free to improve:
> 
> 	Introduce the "io_alloc" resctrl file to the "info" area of a cache
> 	resource, for example /sys/fs/resctrl/info/L3/io_alloc. "io_alloc"
> 	indicates support for the "io_alloc" feature that allows direct
> 	insertion of data from I/O devices into the cache.
>                                                                                  
> 	Restrict exposing support for "io_alloc" to the L3 resource that is the
> 	only resource where this feature can be backed by AMD's L3 Smart Data Cache
> 	Injection Allocation Enforcement (SDCIAE). With that, the "io_alloc" file is only
> 	visible to user space if the L3 resource supports "io_alloc". Doing
> 	so makes the file visible for all cache resources though, for example also L2
> 	cache (if it supports cache allocation). As a consequence, add capability for
> 	file to report expected "enabled" and "disabled", as well as "not supported".
> 
> 

Looks good. Thanks

>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> 
> ...
> 
>> ---
>>   Documentation/filesystems/resctrl.rst | 30 +++++++++++++++++++++++++++
>>   fs/resctrl/ctrlmondata.c              | 21 +++++++++++++++++++
>>   fs/resctrl/internal.h                 |  5 +++++
>>   fs/resctrl/rdtgroup.c                 | 24 ++++++++++++++++++++-
>>   4 files changed, 79 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>> index 4866a8a4189f..89aab17b00cb 100644
>> --- a/Documentation/filesystems/resctrl.rst
>> +++ b/Documentation/filesystems/resctrl.rst
>> @@ -136,6 +136,36 @@ 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":
>> +			      Resource supports "io_alloc" but the feature is disabled.
>> +			      Portions of cache used for allocation of I/O traffic cannot
>> +			      be configured.
>> +			"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.
>> +
> 
> After trying to rework the changelogs I believe the portion of doc below is better suited for
> the next patch that adds support for enable/disable where CLOSIDs are relevant.

Sure.

Thanks
Babu
> 
>> +		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, io_alloc feature is supported by the L3 Smart
>> +		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:
>>   
> 
> Reinette
> 
>