Re: [Xen-devel] Re: Xen scheduler

[Emmanuel Ackaouy <ackaouy@xxxxxxxxx>]

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.

Cheers,
Emmanuel.

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