Re: [PATCHv6 07/10] acpi/hmat: Register processor domain to its memory

On Wed, Feb 20, 2019 at 11:44 PM Keith Busch [off-list ref] wrote:

On Wed, Feb 20, 2019 at 11:21:45PM +0100, Rafael J. Wysocki wrote:

quoted

On Wed, Feb 20, 2019 at 11:11 PM Dave Hansen [off-list ref] wrote:

quoted

On 2/20/19 2:02 PM, Rafael J. Wysocki wrote:

quoted

quoted

diff --git a/drivers/acpi/hmat/Kconfig b/drivers/acpi/hmat/Kconfig
index c9637e2e7514..08e972ead159 100644
--- a/drivers/acpi/hmat/Kconfig
+++ b/drivers/acpi/hmat/Kconfig

@@ -2,6 +2,7 @@
 config ACPI_HMAT
        bool "ACPI Heterogeneous Memory Attribute Table Support"
        depends on ACPI_NUMA
+       select HMEM_REPORTING

If you want to do this here, I'm not sure that defining HMEM_REPORTING
as a user-selectable option is a good idea.  In particular, I don't
really think that setting ACPI_HMAT without it makes a lot of sense.
Apart from this, the patch looks reasonable to me.

I guess the question is whether we would want to allow folks to consume
the HMAT inside the kernel while not reporting it out via
HMEM_REPORTING.  We have some in-kernel users of the HMAT lined up like
mitigations for memory-side caches.

It's certainly possible that folks would want to consume those
mitigations without anything in sysfs.  They might not even want or need
NUMA support itself, for instance.

So, what should we do?

config HMEM_REPORTING
        bool # no user-visible prompt
        default y if ACPI_HMAT

So folks can override in their .config, but they don't see a prompt?

Maybe it would be better to make HMEM_REPORTING do "select ACPI_HMAT if ACPI".

The mitigations could then do that too if they depend on HMAT and
ACPI_HMAT need not be user-visible at all.

That sounds okay, though it would create unreachable code if !ACPI since
that's the only user for the new reporting interfaces.

Until there are other users of it, you can make HMEM_REPORTING depend
on ACPI_NUMA and select ACPI_HMAT.