On Wed, 13 Nov 2019 08:52:46 -0800
Dan Williams [off-list ref] wrote:

On Wed, Nov 13, 2019 at 5:57 AM Tao Xu [off-list ref] wrote:

quoted

On 11/13/2019 5:47 PM, Jonathan Cameron wrote:  

quoted

On Tue, 12 Nov 2019 09:55:17 -0800
Dan Williams [off-list ref] wrote:
 

quoted

[ add Tao Xu ]

On Fri, Oct 4, 2019 at 4:45 AM Jonathan Cameron
[off-list ref] wrote:  

quoted

Generic Initiators are a new ACPI concept that allows for the
description of proximity domains that contain a device which
performs memory access (such as a network card) but neither
host CPU nor Memory.

This patch has the parsing code and provides the infrastructure
for an architecture to associate these new domains with their
nearest memory processing node.  

Thanks for this Jonathan. May I ask how this was tested? Tao has been
working on qemu support for HMAT [1]. I have not checked if it already
supports generic initiator entries, but it would be helpful to include
an example of how the kernel sees these configurations in practice.

[1]: http://patchwork.ozlabs.org/cover/1096737/  

Tested against qemu with SRAT and SLIT table overrides from an
initrd to actually create the node and give it distances
(those all turn up correctly in the normal places).  DSDT override
used to move an emulated network card into the GI numa node.  That
currently requires the PCI patch referred to in the cover letter.
On arm64 tested both on qemu and real hardware (overrides on tables
even for real hardware as I can't persuade our BIOS team to implement
Generic Initiators until an OS is actually using them.)

Main real requirement is memory allocations then occur from one of
the nodes at the minimal distance when you are do a devm_ allocation
from a device assigned. Also need to be able to query the distances
to allow load balancing etc.  All that works as expected.

It only has a fairly tangential connection to HMAT in that HMAT
can provide information on GI nodes.  Given HMAT code is quite happy
with memoryless nodes anyway it should work.  QEMU doesn't currently
have support to create GI SRAT entries let alone HMAT using them.

Whilst I could look at adding such support to QEMU, it's not
exactly high priority to emulate something we can test easily
by overriding the tables before the kernel reads them.

I'll look at how hard it is to build an HMAT tables for my test
configs based on the ones I used to test your HMAT patches a while
back.  Should be easy if tedious.

Jonathan
 

Indeed, HMAT can support Generic Initiator, but as far as I know, QEMU
only can emulate a node with cpu and memory, or memory-only. Even if we
assign a node with cpu only, qemu will raise error. Considering
compatibility, there are lots of work to do for QEMU if we change NUMA
or SRAT table.  

Thanks for the background. It would still be a useful feature to be
able to define a memory + generic-initiator node in qemu. That will
mirror real world accelerators with local memory configurations.

Ah crossed with my essay.  This simple case you have here is easier to
discuss.  Lets call it a GPU on a coherent interconnect with local memory.

What do you think should happen for access0 in sysfs?  Do we want the
GPU reflected in there or not?

This particular case doesn't actually need a GI, though perhaps you
might want one purely to give HMAT based info.  On a pre GI system
you would just use a memory only node and use DSDT _PXM to put the
GPU device in it.

Whilst I agree a means of testing this in qemu might be more
friendly than doing it by overriding tables, the overriding route
lets you do the crazy corner cases + generate 'invalid' tables
which are also useful for testing.

Thanks,

Jonathan



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