Re: [PATCH] x86/PCI: initialize PCI bus node numbers early

Jesse Brandeburg
2009-07-14T07:41:32Z

On Fri, Jul 10, 2009 at 2:06 PM, Jesse Barnes<jbarnes@virtuousgeek.org> wrote:
> From 2b51fba93f7b2dabf453a74923a9a217611ebc1a Mon Sep 17 00:00:00 2001
> From: Jesse Barnes <jbarnes@virtuousgeek.org>
> Date: Fri, 10 Jul 2009 14:04:30 -0700
> Subject: [PATCH] x86/PCI: initialize PCI bus node numbers early
>
> The current mp_bus_to_node array is initialized only by AMD specific
> code, since AMD platforms have registers that can be used for
> determining mode numbers.  On new Intel platforms it's necessary to
> initialize this array as well though, otherwise all PCI node numbers
> will be 0, when in fact they should be -1 (indicating that I/O isn't
> tied to any particular node).
>
> So move the mp_bus_to_node code into the common PCI code, and
> initialize it early with a default value of -1.  This may be overridden
> later by arch code (e.g. the AMD code).
>
> With this change, PCI consistent memory and other node specific
> allocations (e.g. skbuff allocs) should occur on the "current" node.
> If, for performance reasons, applications want to be bound to specific
> nodes, they should open their devices only after being pinned to the
> CPU where they'll run, for maximum locality.
>
> Acked-by: Yinghai Lu <yinghai@kernel.org>
> Tested-by: Jesse Brandeburg <jesse.brandeburg@gmail.com>
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

I can confirm this works, aside from the MSI-X interrupt migration
instability (panics) that I believe are unrelated since they happen
without this patch.

I also see a pretty nice performance boost by running with this change
on a 5520 motherboard, with an 82599 10GbE forwarding packets, esp
with interrupt affinity set correctly.

I'd like to see this applied if at all possible, I think it is really
hampering I/O traffic performance due to limiting all network (among
others) memory allocation to one of the two numa nodes.