Re: [PATCH V6 0/7] ACPI: Support Generic Initiator proximity domains

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Brice Goglin <brice.goglin@gmail.com>
Cc: <linux-mm@kvack.org>, <linux-acpi@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>, <x86@kernel.org>,
	Keith Busch <kbusch@kernel.org>, <jglisse@redhat.com>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>, <linuxarm@huawei.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Tao Xu <tao3.xu@intel.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Hanjun Guo <guohanjun@huawei.com>,
	Sudeep Holla <sudeep.holla@arm.com>
Subject: Re: [PATCH V6 0/7] ACPI: Support Generic Initiator proximity domains
Date: Fri, 3 Jan 2020 13:08:50 +0000	[thread overview]
Message-ID: <20200103130850.00000ace@Huawei.com> (raw)
In-Reply-To: <13b2cc22-df30-ebee-fb94-cd66d8334507@gmail.com>

On Fri, 3 Jan 2020 13:18:59 +0100
Brice Goglin <brice.goglin@gmail.com> wrote:

> Le 03/01/2020 à 11:09, Jonathan Cameron a écrit :
> >
> > 1) If the memory and processor are in the same domain, that should mean the
> > access characteristics within that domain are the best in the system.
> > It is possible to have a setup with very low latency access
> > from a particular processor but also low bandwidth.  Another domain may have
> > high bandwidth but long latency.   Such systems may occur, but they are probably
> > going to not be for 'normal memory the OS can just use'.
> >
> > 2) If we have a relevant "Memory Proximity Domain Attributes Structure"
> > Note this was renamed in acpi 6.3 from "Address Range Structure" as
> > it no longer has any address ranges.
> > (which are entirely optional btw) that indicates that the memory controller
> > for a given memory lies in the proximity domain of the Initiator specified.
> > If that happens we ignore cases where hmat says somewhere else is nearer
> > via bandwidth and latency.
> >
> > For case 1) I'm not sure we actually enforce it.
> > I think you've hit case 2).  
> >
> > Removing the address range structures should work, or as you say you can
> > move that memory into separate memory nodes.  
> 
> 
> I removed the "processor proximity domain valid" flag from the address
> range structure of node2, and the GI is now its access0 initiator
> instead of node2 itself. Looks like it confirms I was in case 2)
> 
> Thanks
> 
> Brice

Cool. I was wondering if that change would work fine.
It is a somewhat crazy setup so I didn't have an equivalent in my test set.

Sounds like all is working as expected.

Thanks,

Jonathan