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Date: Tue, 12 Mar 2024 10:15:32 -0700
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Subject: Re: [PATCH v2 00/17] x86/resctrl : Support AMD Assignable Bandwidth
 Monitoring Counters (ABMC)
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To: <babu.moger@amd.com>, James Morse <james.morse@arm.com>, <corbet@lwn.net>,
	<fenghua.yu@intel.com>, <tglx@linutronix.de>, <mingo@redhat.com>,
	<bp@alien8.de>, <dave.hansen@linux.intel.com>
CC: <x86@kernel.org>, <hpa@zytor.com>, <paulmck@kernel.org>,
	<rdunlap@infradead.org>, <tj@kernel.org>, <peterz@infradead.org>,
	<yanjiewtw@gmail.com>, <kim.phillips@amd.com>, <lukas.bulwahn@gmail.com>,
	<seanjc@google.com>, <jmattson@google.com>, <leitao@debian.org>,
	<jpoimboe@kernel.org>, <rick.p.edgecombe@intel.com>,
	<kirill.shutemov@linux.intel.com>, <jithu.joseph@intel.com>,
	<kai.huang@intel.com>, <kan.liang@linux.intel.com>,
	<daniel.sneddon@linux.intel.com>, <pbonzini@redhat.com>,
	<sandipan.das@amd.com>, <ilpo.jarvinen@linux.intel.com>,
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	<eranian@google.com>
References: <20231201005720.235639-1-babu.moger@amd.com>
 <cover.1705688538.git.babu.moger@amd.com>
 <2f373abf-f0c0-4f5d-9e22-1039a40a57f0@arm.com>
 <474ebe02-2d24-4ce3-b26a-46c520efd453@amd.com>
 <b6bb6a59-67c2-47bc-b8d3-04cf8fd21219@intel.com>
 <3fe3f235-d8a6-453b-b69d-6b7f81c07ae1@amd.com>
 <9b94b97e-4a8c-415e-af7a-d3f832592cf9@intel.com>
 <1ae73c9a-cec4-4496-86c6-3ffcef7940d6@amd.com>
 <32a588e2-7b09-4257-b838-4268583a724d@intel.com>
 <088878bd-7533-492d-838c-6b39a93aad4d@amd.com>
 <9b20589b-6220-4ae7-bfc4-4a826b7114b1@intel.com>
 <4b3418ed-751d-4e37-8d72-f2b4891eb714@amd.com>
 <d594a7e0-e33e-4311-8079-14dd56f6d309@intel.com>
 <34e48584-dd0f-47ce-b6e6-fad970546cca@amd.com>
From: Reinette Chatre <reinette.chatre@intel.com>
In-Reply-To: <34e48584-dd0f-47ce-b6e6-fad970546cca@amd.com>
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Hi Babu,

On 3/12/2024 10:07 AM, Moger, Babu wrote:
> On 3/12/24 10:13, Reinette Chatre wrote:
>> On 3/11/2024 8:40 AM, Moger, Babu wrote:
>>> On 2/27/24 17:50, Reinette Chatre wrote:
>>>> On 2/27/2024 10:12 AM, Moger, Babu wrote:
>>>>> On 2/26/24 15:20, Reinette Chatre wrote:
>>>>>> On 2/26/2024 9:59 AM, Moger, Babu wrote:
>>>>>>> On 2/23/24 16:21, Reinette Chatre wrote:
>>>>
>>>>>>>> Apart from the "default behavior" there are two options to consider ...
>>>>>>>> (a) the "original" behavior(? I do not know what to call it) - this would be
>>>>>>>>     where user space wants(?) to have the current non-ABMC behavior on an ABMC
>>>>>>>>     system, where the previous "num_rmids" monitor groups can be created but
>>>>>>>>     the counters are reset unpredictably ... should this still be supported
>>>>>>>>     on ABMC systems though?
>>>>>>>
>>>>>>> I would say yes. For some reason user(hardware or software issues) is not
>>>>>>> able to use ABMC mode, they have an option to go back to legacy mode.
>>>>>>
>>>>>> I see. Should this perhaps be protected behind the resctrl "debug" mount option?
>>>>>
>>>>> The debug option gives wrong impression. It is better to keep the option
>>>>> open to enable the feature in normal mode.
>>>>
>>>> You mentioned that it would only be needed when there are hardware or
>>>> software issues ... so debug does sound appropriate. Could you please give
>>>> an example of how debug option gives wrong impression? Why would you want
>>>> users to keep using "legacy" mode on an ABMC system?
>>>
>>> We may not be able to use "-o debug" option to enable "legacy_mbm".
>>> With debug option it will always go to legcay mbm even if ABMC is supported.
>>>
>>> For example when ABMC is supported, I cannot mount the resctrl with debug
>>> option to test ABMC.
>>>
>>> I need to have a way to mount resctrl with ABMC and debug option. I can
>>> add "-o legacy_mbm" to enable lecacy_mbm.
>>
>> I do not think it is necessary to add a unique debug option for this.
> 
> It makes the code simple.
> 
>> What if instead the "-o debug" mount option exposes the "original/legacy"
> 
> Can you please elaborate on this?
> 
> Did you mean following command to enable legacy mode?
> 
> $echo "original/legacy"    /sys/fs/resctrl/info/L3_MON/mbm_assign_control
> 
> It feels like a overkill and confusing.

I used the "original/legacy" text to make it clear which behavior I was
referring to. It was not a proposal for a label used by user space to 
select the behavior.

Isn't /sys/fs/resctrl/info/L3_MON/mbm_assign_control the file that will
assign the counters to domains? That should not be the file used to 
select the behavior. You had /sys/fs/resctrl/info/L3_MON/mbm_assign
with which user space selects behavior, no?


Reinette