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

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Date:   Fri, 3 Jan 2020 13:18:59 +0100
From:   Brice Goglin <brice.goglin@...il.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     linux-mm@...ck.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org, Keith Busch <kbusch@...nel.org>,
        jglisse@...hat.com, "Rafael J . Wysocki" <rjw@...ysocki.net>,
        linuxarm@...wei.com, Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Tao Xu <tao3.xu@...el.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH V6 0/7] ACPI: Support Generic Initiator proximity domains

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