Re: [Xen-users] Xen Performance

Luke S Crawford
Tue, 02 Jun 2009 05:59:41 -0000

Adam Wead <awead@indiana.edu> writes:

> On Jun 1, 2009, at 8:43 PM, Luke S Crawford wrote:
> >
> >
> > Also note, I''ve seen better worst-case performance by giving
each
> > VM fewer
> > VCPUs, and the xen guys are not kidding about dedicating a core to the
> > Dom0.   setting cpus="1-7" in your xm config file (assuming
an 8
> > core box)
> > and giving dom0 only 1 vcpu makes a world of difference on heavily
> > loaded boxes.
> >
>
> This may be a dumb question, but is that any different from or the
> same as setting "dom0-cpus 1" in the xend-config.sxp file?  Are
you
> specifying "cpus=1-7" in the guest''s config or the Xen
daemon''s config?

> thanks in advance for clearing up my confusion,

setting cpus="1-7" in the guest config file is important, because
otherwise
the guests will run on all cpus, including the dom0 cpus.

I believe the dom0 vcp0 is pinned to cpu0, vcpu1 is pinned to cpu1 .... so
setting dom0-cpus 1  will pin the dom0 cpu 0 to 0.


just setting dom0-cpus in xend-config.sxp without setting cpus= in the domu
configs doesn''t help much, because the guests still trample over the
one
cpu the dom0 has.