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Re: [Xen-devel] numa=on broken

  • To: Ryan Harper <ryanh@xxxxxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Sat, 31 Mar 2007 10:06:44 +0100
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Sat, 31 Mar 2007 10:07:31 +0100
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: Acdzc+coJbNsPN9nEdufvgAWy6hiGQ==
  • Thread-topic: [Xen-devel] numa=on broken

On 30/3/07 20:39, "Ryan Harper" <ryanh@xxxxxxxxxx> wrote:

>> Turning on by default is pointless because guests are not restricted to
>> running on specific nodes by default. Since manual intervention is required
>> to achieve that (right now at least) requiring numa=on is not much of a
>> hardship.
> I'm getting ready to re-submit patches to export the topology information
> so the userspace tools can use that info to make intelligent selections.
> This was available back in October, but was never picked up, or even
> commented upon.

But can tools make sane automatic decisions on domain creation? And if tools
decide not to use NUMA-ness of the system, should the Xen allocator still
hoover up all the memory of the node that vcpu0 happens to start on?

My primary concern is simply whether enabling NUMA by default can hurt
performance, or cause problems by hitting certain memory nodes or memory
zones harder than others, for the great majority of users who will not use
NUMA (even if they have a small NUMA system like AMD K8).

 -- Keir

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