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Re: [Xen-devel] Re: Xen scheduler

  • To: pak333@xxxxxxxxxxx
  • From: Emmanuel Ackaouy <ackaouy@xxxxxxxxx>
  • Date: Tue, 24 Apr 2007 16:34:43 +0200
  • Cc: ncmike@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Tue, 24 Apr 2007 07:33:40 -0700
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On Apr 23, 2007, at 21:33, pak333@xxxxxxxxxxx wrote:
Basically all my questions boil down to this: Does the Scheduler know about the pcpu layout(same socket) and does it do any scheduling based on that.

Yes but not how you suggested.

The scheduler actually tries to schedule VCPUs across multiple
sockets before it "co-schedules" a socket. The idea behind this is
to maximize the achievable memory bandwidth.

On hyperthreaded systems, the scheduler will also attempt to
schedule across cores before it co-schedules hyperthreads. This
is to maximize achievable cycles.

At this time, no attempt is made to schedule 2 VCPUs of the
same VM any differently than 2 VCPUs of distinct VMs.

If you feel two VCPUs would do better co-scheduled on a
core or socket, you'd currently have to use cpumasks -- as
mike suggested -- to restrict where they can run manually. I'd
be curious to know of real world cases where doing this
increases performance significantly.

Hope this helps.


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