Re: dom0 -> domU packet loss

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sun, May 03, 2009 at 07:47:46PM -0400, Brian Marcotte wrote:
> > did you get any more details about this ? Any patch ?
> 
> The patch I'm currently using is below. It does prevent the drops in the
> (Linux) domU, but I'm no longer able to test it on the one machine which
> eventually slowed to a crawl with the earlier version of the patch. All
> other machines are doing fine.
> 
> It's been difficult for me to determine if this is the right thing or
> not. I've not yet found documentation or discussion on how the network
> drivers are supposed to work.
> 
> I tried out iperf. The interesting thing is that my results were
> largely the same against a Xen domU and hardware. I can saturate a 100 mb
> ethernet with TCP, but with UDP half the packets are dropped somewhere.
> 
> Increasing net.inet.udp.recvspace/sendspace helps.

Yes of course; with a protocol without flow control, you will overflow
the socket buffer, then the network send queue.
This may be a difference between NetBSD and linux: linux may block when the
socket buffer is full while NetBSD may drop the paquets.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--