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

From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Keith Busch <keith.busch@intel.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	Linux API <linux-api@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCHv6 07/10] acpi/hmat: Register processor domain to its memory
Date: Sun, 24 Feb 2019 21:07:03 +0100	[thread overview]
Message-ID: <CAJZ5v0gyEJ59qSno_MKjr97zeYaLp=v1=ZYz1twM1eZJCP_DTw@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4jpP0CP-QxWDc_E1QwL736PLwh8ZPrnKJzVnYrAk++93g@mail.gmail.com>

On Fri, Feb 22, 2019 at 8:21 PM Dan Williams <dan.j.williams@intel.com> wrote:
>
> On Fri, Feb 22, 2019 at 10:48 AM Keith Busch <keith.busch@intel.com> wrote:
> >
> > On Wed, Feb 20, 2019 at 11:02:01PM +0100, Rafael J. Wysocki wrote:
> > > On Thu, Feb 14, 2019 at 6:10 PM Keith Busch <keith.busch@intel.com> wrote:
> > > >  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'm trying to implement based on the feedback, but I'm a little confused.
> >
> > As I have it at the moment, HMEM_REPORTING is not user-prompted, so
> > another option needs to turn it on. I have ACPI_HMAT do that here.
> >
> > So when you say it's a bad idea to make HMEM_REPORTING user selectable,
> > isn't it already not user selectable?
> >
> > If I do it the other way around, that's going to make HMEM_REPORTING
> > complicated if a non-ACPI implementation wants to report HMEM
> > properties.
>
> Agree. If a platform supports these HMEM properties then they should
> be reported.

Well, I'm not sure if everybody is in agreement on that.

> ACPI_HMAT is that opt-in for ACPI based platforms, and
> other archs can do something similar. It's not clear that one would
> ever want to opt-in to HMAT support and opt-out of reporting any of it
> to userspace.

In my view, ACPI_HMAT need not be an opt-in in the first place.  The
only reason to avoid compiling HMAT parsing it would be if there were
no users of it in the kernel IMO.