linux-kernel - Re: [RFC PATCH v3 00/17] x86/resctrl : Support AMD Assignable Bandwidth Monitoring Counters (ABMC)

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Message-ID: <CALPaoCiu2_UHyGjsyitz28BL1N93TSn28E1r-6nhXg--bzmU+Q@mail.gmail.com>
Date: Fri, 3 May 2024 14:00:21 -0700
From: Peter Newman <peternewman@...gle.com>
To: babu.moger@....com
Cc: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net, fenghua.yu@...el.com, 
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
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Subject: Re: [RFC PATCH v3 00/17] x86/resctrl : Support AMD Assignable
 Bandwidth Monitoring Counters (ABMC)

Hi Babu,

On Fri, May 3, 2024 at 1:44 PM Moger, Babu <bmoger@....com> wrote:
>
> Hi Peter,
>
> On 5/2/2024 7:57 PM, Peter Newman wrote:
> > Hi Reinette,
> >
> > On Thu, May 2, 2024 at 4:21 PM Reinette Chatre
> >> I do think ABMC should be enabled by default when available and it looks
> >> to be what this series aims to do [1]. The way I reason about this is
> >> that legacy user space gets more reliable monitoring behavior without
> >> needing to change behavior.
> >
> > I don't like that for a monitor assignment-aware user, following the
> > creation of new monitoring groups, there will be less monitors
> > available for assignment. If the user wants precise control over where
> > monitors are allocated, they would need to manually unassign the
> > automatically-assigned monitor after creating new groups.
> >
> > It's an annoyance, but I'm not sure if it would break any realistic
> > usage model. Maybe if the monitoring agent operates independently of
>
> Yes. Its annoyance.
>
> But if you think about it, normal users don't create too many groups.
> They wont have to worry about assign/unassign headache if we enable
> monitor assignment automatically. Also there is pqos tool which uses
> this interface. It does not have to know about assign/unassign stuff.

Thinking about this again, I don't think it's much of a concern
because the automatic assignment on mongroup creation behavior can be
trivially disabled using a boolean flag.

-Peter