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

From: Brice Goglin <brice.goglin@gmail.com>
To: Jonathan Cameron <Jonathan.Cameron@Huawei.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 13:18:59 +0100	[thread overview]
Message-ID: <13b2cc22-df30-ebee-fb94-cd66d8334507@gmail.com> (raw)
In-Reply-To: <20200103100920.00006a18@Huawei.com>

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