Re: [Xen-devel] Buffered IO for IO?

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 23/7/07 20:38, "Zulauf, John" <john.zulauf@xxxxxxxxx> wrote:

> I'm running on an 8-core system with currently only two HVM domains
> (with currently single VCPU each). Both top on Dom0 and xm top, don't
> seem to indicate qemu-dm as the performance bottleneck.  However, I'm
> not sure about roundtrip latency through the xenstore to qemu and back.

Well, maybe you are just seeing VMEXIT time then. You might try adding some
RDTSC from when a notification is sent to qemu until when your HVM vcpu is
rewoken, and see what the latency looks like. It shouldn't be all that bad
if dom0 is on another cpu and is otherwise fairly idle.

Also, you could see how many characters are sent and received to start a
windbg session. If there are a surprisingly large number of bytes received
then it may be the receive direction is causing more trouble than the
transmit direction.

 -- Keir


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