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xen-devel
[Xen-devel] Re: credit scheduler
On Mon, Aug 28, 2006 at 05:28:08PM -0500, Karl Rister wrote:
> While doing some performance analysis of Xen I have noticed some interesting
> behavior of the credit scheduler that I would like to see discussed.
>
> In my most basic test I have a 4 socket dual core Intel box (Paxville) with a
> uniprocessor dom0 and 7 uniprocessor domUs. Each of the domUs is pinned on
> its own core with the first core of the system left for dom0. When running
> the credit scheduler the dom0 VCPU will bounce around the system, sometimes
> landing on the same thread as one of the domUs or sometimes on one of the
> sibling hyperthreads (this appears to happen a majority of the time it
> moves). This is less than ideal when considering cache warmth and the
> sharing of CPU resources when the first core of the system is always
> available in this configuration. Does the credit scheduler have any
> awareness of cache warmth or CPU siblings when balancing?
A related issue I noticed the other day when doing xen testing off of
xen-unstable was that the irqbalancer process ended up consuming 100% of
dom0 cpu when running an SMP Dom0 on the credit scheduler, and a bunch of
idle domUs. It got the the point that ssh wasn't feasable, and I had to go
to the console and shut off irqbalancer to return things to normal.
I'd follow up further, but I'm about to go "off grid" for the next 2.5
weeks. I relayed information to other folks on the IBM team to see if
anyone else can reproduce it.
-Sean
--
Sean Dague
IBM Linux Technology Center email: japh@xxxxxxxxxx
Open Hypervisor Team alt: sldague@xxxxxxxxxx
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