RE: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> There have been a couple of network receive throughput 
> performance regressions to domUs over time that were 
> subsequently fixed. I think one may have crept in to 3.0.3.

The report was (I believe) with a NIC directly assigned to the domU, so
not using netfront/back at all.

John: please can you give more details on your config.

Ian
 
> Are you seeing any dropped packets on the vif associated with 
> your domU in your dom0? If so, propagating changeset
> 11861 from unstable may help:
> 
> changeset:   11861:637eace6d5c6
> user:        kfraser@xxxxxxxxxxxxxxxxxxxxx
> date:        Mon Oct 23 11:20:37 2006 +0100
> summary:     [NET] back: Fix packet queuing so that packets 
> are drained if the
> 
> 
> In the past, we also had receive throughput issues to domUs 
> that were due to socket buffer size logic but those were 
> fixed a while ago.
> 
> Can you send netstat -i output from dom0?
> 
> Emmanuel.
> 
> 
> On Mon, Nov 06, 2006 at 09:55:17PM -0800, John Byrne wrote:
> > 
> > I was asked to test direct I/O to a PV domU. Since, I had a system 
> > with two NICs, I gave one to a domU and one dom0. (Each is 
> running the 
> > same
> > kernel: xen 3.0.3 x86_64.)
> > 
> > I'm running netperf from an outside system to the domU and 
> dom0 and I 
> > am seeing 30% less throughput for the domU vs dom0.
> > 
> > Is this to be expected? If so, why? If not, does anyone 
> have a guess 
> > as to what I might be doing wrong or what the issue might be?
> > 
> > Thanks,
> > 
> > John Byrne
> 
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