Re: [PATCH v3 0/3] create sysfs representation of ACPI HMAT

From: Michael Ellerman
Date: Thu Dec 21 2017 - 07:50:51 EST

Matthew Wilcox <willy@xxxxxxxxxxxxx> 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.