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Date:   Thu, 21 Dec 2017 23:50:40 +1100
From:   Michael Ellerman <>
To:     Matthew Wilcox <>,
        Ross Zwisler <>
Cc:     Michal Hocko <>,
        "Box\, David E" <>,
        Dave Hansen <>,
        "Zheng\, Lv" <>,,
        "Verma\, Vishal L" <>,
        "Rafael J. Wysocki" <>,
        "Anaczkowski\, Lukasz" <>,
        "Moore\, Robert" <>,,
        "Odzioba\, Lukasz" <>,
        "Schmauss\, Erik" <>,
        Len Brown <>,
        John Hubbard <>,, Jerome Glisse <>,
        Dan Williams <>,,
        "Kogut\, Jaroslaw" <>,,
        "Koss\, Marcin" <>,,
        Brice Goglin <>,
        "Nachimuthu\, Murugasamy" <>,
        "Rafael J. Wysocki" <>,,
        "Koziej\, Artur" <>,
        "Lahtinen\, Joonas" <>,
        Andrew Morton <>,
        Tim Chen <>
Subject: Re: [PATCH v3 0/3] create sysfs representation of ACPI HMAT

Matthew Wilcox <> writes:

> On Mon, Dec 18, 2017 at 01:35:47PM -0700, Ross Zwisler wrote:
>> What I'm hoping to do with this series is to just provide a sysfs
>> representation of the HMAT so that applications can know which NUMA nodes to
>> select with existing utilities like numactl.  This series does not currently
>> alter any kernel behavior, it only provides a sysfs interface.
>> Say for example you had a system with some high bandwidth memory (HBM), and
>> you wanted to use it for a specific application.  You could use the sysfs
>> representation of the HMAT to figure out which memory target held your HBM.
>> You could do this by looking at the local bandwidth values for the various
>> memory targets, so:
>> 	# grep . /sys/devices/system/hmat/mem_tgt*/local_init/write_bw_MBps
>> 	/sys/devices/system/hmat/mem_tgt2/local_init/write_bw_MBps:81920
>> 	/sys/devices/system/hmat/mem_tgt3/local_init/write_bw_MBps:40960
>> 	/sys/devices/system/hmat/mem_tgt4/local_init/write_bw_MBps:40960
>> 	/sys/devices/system/hmat/mem_tgt5/local_init/write_bw_MBps:40960
>> and look for the one that corresponds to your HBM speed. (These numbers are
>> made up, but you get the idea.)
> Presumably ACPI-based platforms will not be the only ones who have the
> ability to expose different bandwidth memories in the future.  I think
> we need a platform-agnostic way ... right, PowerPC people?


I don't have any detail at hand but will try and rustle something up.


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