linux-kernel - Re: [LSF/MM] CXL Boot to Bash - Section 0: ACPI and Linux Resources

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Message-ID: <Z-V-jXYsOfQDvCzc@gourry-fedora-PF4VCD3F>
Date: Thu, 27 Mar 2025 12:36:29 -0400
From: Gregory Price <gourry@...rry.net>
To: Dan Williams <dan.j.williams@...el.com>
Cc: Yuquan Wang <wangyuquan1236@...tium.com.cn>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	lsf-pc@...ts.linux-foundation.org, linux-mm@...ck.org,
	linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [LSF/MM] CXL Boot to Bash - Section 0: ACPI and Linux Resources

On Thu, Mar 27, 2025 at 09:21:55AM -0400, Dan Williams wrote:
> Gregory Price wrote:
> > On Thu, Mar 27, 2025 at 05:34:54PM +0800, Yuquan Wang wrote:
> > > 
> > > In the future, srat.c would add one seperate NUMA node for each
> > > Generic Port in SRAT.
> > > 
> > > System firmware should know the performance characteristics between
> > > CPU/GI to the GP, and the static HMAT should include this coordinate.
> > > 
> > > Is my understanding right?
> > > 
> > > 
> > 
> > HMAT is static configuration data.  A GI/GP might not have its
> > performance data known until the device is added.
> 
> The GP data is static and expected to be valid for all host bridges in
> advance of any devices arriving.
>

Sorry, just shuffling words here for clarity.  Making sure I understand:

The GP data is static and enables Linux to do things like reserve numa
nodes for any devices might arrive in the future (i.e. create static
objects that cannot be created post-__init).

If there's no device, there should not be any HMAT data.  If / when a
device arrives, it's up to the OS to acquire that information from the
device (e.g. CDAT).  At this point the ACPI tables are not (shouldn't
be) involved - it's all OS/device interactions.

I should note that I don't have a full grasp of the GP ACPI stuff yet,
so doing my best to grok it as I go here.

~Gregory