linux-kernel - Re: [PATCH v2 05/18] x86/resctrl: Allow RMID allocation to be scoped by CLOSID

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Date:   Fri, 10 Mar 2023 11:57:48 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     James Morse <james.morse@....com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Babu Moger <Babu.Moger@....com>,
        <shameerali.kolothum.thodi@...wei.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        <carl@...amperecomputing.com>, <lcherian@...vell.com>,
        <bobo.shaobowang@...wei.com>, <tan.shaopeng@...itsu.com>,
        <xingxin.hx@...nanolis.org>, <baolin.wang@...ux.alibaba.com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, <peternewman@...gle.com>
Subject: Re: [PATCH v2 05/18] x86/resctrl: Allow RMID allocation to be scoped
 by CLOSID

Hi James,

On 3/3/2023 10:34 AM, James Morse wrote:
> On 02/02/2023 23:45, Reinette Chatre wrote:
>> On 1/13/2023 9:54 AM, James Morse wrote:

...

>>>  /*
>>> - * As of now the RMIDs allocation is global.
>>> + * As of now the RMIDs allocation is the same in each domain.
> 
>> Could you please elaborate what is meant/intended with this change
>> (global vs per domain)? From the changelog a comment that RMID
>> allocation is the same in each resource group for MPAM may be
>> expected but per domain is not clear to me.
> 
> This is badly worded. It's referring to the limbo list management, while RMID=7 isn't
> unique on MPAM, the struct rmid_entry used in two domains will be the same because the
> CLOSID doesn't change. This means its still sufficient to move around the struct
> rmid_entry to manage the limbo list.
> 
> I think this had me confused because 'as of now' implies the RMID won't always be globally
> allocated, and MPAM has non-unique RMID/PMG values which are a different kind of global.
> 
> 
> I'll change this to read:
> /*
>  * For MPAM the RMID value is not unique, and has to be considered with
>  * the CLOSID. The (CLOSID, RMID) pair is allocated on all domains, which
>  * allows all domains to be managed by a single limbo list.
>  * Each domain also has a rmid_busy_llc to reduce the work of the limbo handler.
>  */
> 
> (seeing as the function doesn't touch rmid_budy_llc, or refer to it by name)
> 

Thank you. This is easier to understand.

Reinette