linux-kernel - Re: [RFC PATCH v3 17/17] x86/resctrl: Introduce interface to modify assignment states of the groups

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Message-ID: <30f2fb65-10ed-4d60-aadf-6727f7a6e404@amd.com>
Date: Thu, 2 May 2024 13:11:32 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 Dave Martin <Dave.Martin@....com>
Cc: corbet@....net, fenghua.yu@...el.com, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
 hpa@...or.com, paulmck@...nel.org, rdunlap@...radead.org, tj@...nel.org,
 peterz@...radead.org, yanjiewtw@...il.com, kim.phillips@....com,
 lukas.bulwahn@...il.com, seanjc@...gle.com, jmattson@...gle.com,
 leitao@...ian.org, jpoimboe@...nel.org, rick.p.edgecombe@...el.com,
 kirill.shutemov@...ux.intel.com, jithu.joseph@...el.com,
 kai.huang@...el.com, kan.liang@...ux.intel.com,
 daniel.sneddon@...ux.intel.com, pbonzini@...hat.com, sandipan.das@....com,
 ilpo.jarvinen@...ux.intel.com, peternewman@...gle.com,
 maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, eranian@...gle.com, james.morse@....com
Subject: Re: [RFC PATCH v3 17/17] x86/resctrl: Introduce interface to modify
 assignment states of the groups

Hi Dave,


On 5/2/24 12:52, Reinette Chatre wrote:
> Hi Dave,
> 
> On 5/2/2024 9:21 AM, Dave Martin wrote:
>> On Thu, Mar 28, 2024 at 08:06:50PM -0500, Babu Moger wrote:
>>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>>> index 2d96565501ab..64ec70637c66 100644
>>> --- a/Documentation/arch/x86/resctrl.rst
>>> +++ b/Documentation/arch/x86/resctrl.rst
>>> @@ -328,6 +328,77 @@ with the following files:
>>>  	 None of events are assigned on this mon group. This is a child
>>>  	 monitor group of the non default control mon group.
>>>  
>>> +	Assignment state can be updated by writing to this interface.
>>> +
>>> +	NOTE: Assignment on one domain applied on all the domains. User can
>>> +	pass one valid domain and assignment will be updated on all the
>>> +	available domains.
>>> +
>>> +	Format is similar to the list format with addition of op-code for the
>>> +	assignment operation.
>>> +
>>> +        * Default CTRL_MON group:
>>> +                "//<domain_id><op-code><assignment_flags>"
>>> +
>>> +        * Non-default CTRL_MON group:
>>> +                "<CTRL_MON group>//<domain_id><op-code><assignment_flags>"
>>> +
>>> +        * Child MON group of default CTRL_MON group:
>>> +                "/<MON group>/<domain_id><op-code><assignment_flags>"
>>> +
>>> +        * Child MON group of non-default CTRL_MON group:
>>> +                "<CTRL_MON group>/<MON group>/<domain_id><op-code><assignment_flags>"
>>
>> The final bullet seems to cover everything, if we allow <CTRL_MON group>
>> and <MON group> to be independently empty strings to indicate the
>> default control and/or monitoring group respectively.
>>
>> Would that be simpler than treating this as four separate cases?

That is correct. I will add a generic format before this description and
then add these 4 cases. That way it will be more clear.


>>
>> Also, will this go wrong if someone creates a resctrl group with '\n'
>> (i.e., a newline character) in the name?
> 
> There is a check for this in rdtgroup_mkdir().
> 
>>
>>> +
>>> +	Op-code can be one of the following:
>>> +	::
>>> +
>>> +	 = Update the assignment to match the flags
>>> +	 + Assign a new state
>>> +	 - Unassign a new state
>>> +	 _ Unassign all the states
>>
>> I can't remember whether I already asked this, but is "_" really
>> needed here?
> 
> Asked twice:
> https://lore.kernel.org/lkml/ZiaRXrmDDjc194JI@e133380.arm.com/
> https://lore.kernel.org/lkml/ZiervIprcwoApAqw@e133380.arm.com/
> 
> Answered:
> https://lore.kernel.org/lkml/4cd220cc-2e8e-4193-b01a-d3cd798c7118@amd.com/
> 
> You seemed ok with answer then:
> https://lore.kernel.org/lkml/ZiffF93HM8bE3qo7@e133380.arm.com/
> 
>>
>> Wouldn't it be the case that
>>
>> 	//*_
>>
>> would mean just the same thing as
>>
>> 	//*=_
>>
>> ...?  (assuming the "*" = "all domains" convention already discussed)
>>
>> Maybe I'm missing something here.
> 
> I believe have an explicit operator ("+", "=", or "-") simplifies
> parsing while providing an interface consistent with what users are already
> used to.
> 
> Reinette

-- 
Thanks
Babu Moger