Re: Paravirtualised drivers for fully virtualised domains, rev9

[Steven Smith <sos22-xen@srcf.ucam.org>]

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> > > Looks like I jumped the gun in relating the 99.9% CPU usage for qemu-dm
> and
> > > the network.  I start up the HVM domain and without running any tests
> > > qemu-dm is chewing up 99.9% of the CPU in dom0.  So it appears that the
> > > 100% CPU qemu usage is a problem by itself.  Looks like the same
> problem
> > > Harry Butterworth is seeing.
> > qemu-dm misbehaving could certainly lead to the netif going very
> > slowly.
> Agreed.  I applied the patch to sent to Harry.  I appears to fix the 99.9%
> CPU usage problem.
Great, thanks.

> > > > 2) How often is the event channel interrupt firing according to
> > > >    /proc/interrupts?  I see about 50k-150k/second.
> > > I'm seeing ~ 500/s when netpipe-tcp reports decent throughput at
> smaller
> > > buffer sizes and then ~50/s when the throughput drops at larger buffer
> > > sizes.
> > How large do they have to be to cause problems?
> I'm noticing a drop off in throughput at a buffer size of 3069.  Here is a
> snip from the output from netpipe-tcp.
What are the MTUs on the interfaces, according to ifconfig, in dom0
and domU?

> I don't know offhand why the throughput drops off.  I'll look into it.  Any
> tips would be helpful.
tcpdump in the domU and dom0 might be enlightening, just to see if any
packets are getting dropped or truncated.  The connections probably
slow enough when it's misbehaving for it to keep up.

Are you running through the bridge?  It's unlikely to be that, but it
would be good to eliminate it as a variable by doing some domU<->dom0
tests without it involved.

What version of Linux are you running in the domU?  Does it have any
patches applied?

Steven.

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