From: Mark Rutland <mark.rutland@arm.com>
To: Andrew Jones <drjones@redhat.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>,
andre.przywara@arm.com, qemu-arm@nongnu.org,
kvmarm@lists.cs.columbia.edu
Subject: Re: MPIDR Aff0 question
Date: Fri, 5 Feb 2016 11:00:33 +0000 [thread overview]
Message-ID: <20160205110032.GA19614@leverpostej> (raw)
In-Reply-To: <20160205092353.GA3873@hawk.localdomain>
On Fri, Feb 05, 2016 at 10:23:53AM +0100, Andrew Jones wrote:
> On Thu, Feb 04, 2016 at 06:51:06PM +0000, Marc Zyngier wrote:
> What would the benefit of defining a "socket"?
>
> That's a good lead in for my next question. While I don't believe
> there needs to be any relationship between socket and numa node, I
> suspect on real machines there is, and quite possibly socket == node.
> Shannon is adding numa support to QEMU right now. Without special
> configuration there's no gain other than illusion, but with pinning,
> etc. the guest numa nodes will map to host nodes, and thus passing
> that information on to the guest's kernel is useful. Populating a
> socket/node affinity field seems to me like a needed step. But,
> question time, is it? Maybe not.
I don't think it's necessary.
When using ACPI, NUMA info comes from SRAT+SLIT, and the MPIDR.Aff*
fields do not provide NUMA topology info. I expect the same to be true
with DT using something like numa-distance-map [1].
> Also, the way Linux currently handles non-thread using MPIDRs
> (Aff1:socket, Aff0:core) throws a wrench at the Aff2:socket,
> Aff1:"cluster", Aff0:core(max 16) plan. Either the plan or Linux
> would need to be changed.
The topology can be explicitly overridden in DT using cpu-map [2]. I
don't know what the story for ACPI is.
Mark.
[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-February/404057.html
[2] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/arm/topology.txt?h=v4.5-rc2&id=36f90b0a2ddd60823fe193a85e60ff1906c2a9b3
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next prev parent reply other threads:[~2016-02-05 11:01 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-04 18:38 MPIDR Aff0 question Andrew Jones
2016-02-04 18:51 ` Marc Zyngier
2016-02-05 9:23 ` Andrew Jones
2016-02-05 10:37 ` Marc Zyngier
2016-02-05 12:03 ` [Qemu-arm] " Andrew Jones
2016-02-05 13:02 ` Marc Zyngier
2016-02-05 11:00 ` Mark Rutland [this message]
2016-02-05 12:08 ` Andrew Jones
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