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

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Date: Thu, 2 May 2024 10:52:15 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Dave Martin <Dave.Martin@....com>, Babu Moger <babu.moger@....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 5/2/2024 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?
> 
> 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