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

[Emmanuel Ackaouy <ack@xxxxxxxxxxxxx>]

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.

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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