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: <80c56417-3d74-7d68-1228-9cd944567b4e@amd.com>
Date: Wed, 17 Apr 2024 17:52:18 -0500
From: "Moger, Babu" <bmoger@....com>
To: Peter Newman <peternewman@...gle.com>, babu.moger@....com
Cc: corbet@....net, fenghua.yu@...el.com, reinette.chatre@...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,
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 kirill.shutemov@...ux.intel.com, jithu.joseph@...el.com,
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 daniel.sneddon@...ux.intel.com, pbonzini@...hat.com, sandipan.das@....com,
 ilpo.jarvinen@...ux.intel.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 Peter,

On 4/17/2024 3:56 PM, Peter Newman wrote:
> Hi Babu,
>
> On Wed, Apr 17, 2024 at 12:39 PM Moger, Babu <babu.moger@....com> wrote:
>> On 4/17/24 12:45, Peter Newman wrote:
>>> On Thu, Mar 28, 2024 at 6:10 PM Babu Moger <babu.moger@....com> 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.
>>> How would different assignments to different domains work? If the
>>> allocations are global, then the allocated monitor ID is available to
>>> all domains whether they use it or not.
>> That is correct.
>> [A] Hardware counters(max 2 per group) are allocated at the group level.
>> So, those counters are available to all the domains on that group. I will
>> maintain a bitmap at the domain level. The bitmap will be set on the
>> domains where assignment is applied and IPIs are sent. IPIs will not be
>> sent to other domains.
> Unless the monitor allocation is scoped at the domain level, I don't
> see much point in implementing the per-domain parsing today, as the
> only benefit is avoiding IPIs to domains whose counters you don't plan
> to read.

In that case lets remove the domain specific assignments. We can avoid 
some code complexity.

thanks

Babu