linux-kernel - Re: [PATCH v3 29/47] arm_mpam: resctrl: Pick classes for use as mbm counters

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Message-ID: <CALPaoCh+mRLJEfhKBve3hRf+vHHoObjvWRt74OfpopgtR9g9FQ@mail.gmail.com>
Date: Thu, 15 Jan 2026 16:49:20 +0100
From: Peter Newman <peternewman@...gle.com>
To: Ben Horgan <ben.horgan@....com>
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com, 
	baolin.wang@...ux.alibaba.com, carl@...amperecomputing.com, 
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	jonathan.cameron@...wei.com, kobak@...dia.com, lcherian@...vell.com, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
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	kvmarm@...ts.linux.dev
Subject: Re: [PATCH v3 29/47] arm_mpam: resctrl: Pick classes for use as mbm counters

Hi Ben,

On Mon, Jan 12, 2026 at 6:02 PM Ben Horgan <ben.horgan@....com> wrote:
>
> From: James Morse <james.morse@....com>
>
> resctrl has two types of counters, NUMA-local and global. MPAM has only
> bandwidth counters, but the position of the MSC may mean it counts
> NUMA-local, or global traffic.
>
> But the topology information is not available.
>
> Apply a heuristic: the L2 or L3 supports bandwidth monitors, these are
> probably NUMA-local. If the memory controller supports bandwidth monitors,
> they are probably global.

Are remote memory accesses not cached? How do we know an MBWU monitor
residing on a cache won't count remote traffic?

Thanks,
-Peter