RE: [Xen-users] Slow outgoing IP traffic with PV drivers

[Peter Privat <peter.privat@xxxxxxxxxxxx>]

On Mon, 2009-03-02 at 12:58 +1100, James Harper wrote:
> > Large Segment Offloading is enabled by default, and set to a high value
> > (larger then MTU). Since it seems that the PV driver does not respect the
> > MTU, and does not segment the TCP-data (for better domu-domu speeds?) this
> > causes the bridge (this might be due to a bug in my setup which is gentoo
> > with vanilla xen configuration) to transmit frames that are larger than
> > the supported MTU of the recipients. I haven't yet tried enabling support
> > for jumbo frames on my clients, but still."
> > 
> > James... Are there any more "tunings" possible?
> > 
>
> Not really. All of those offloads will make things go faster if they work, but much much slower if they don't. The idea of LSO is to give the physical network card 64k packets and let it break them into MTU sized chunks. If your linux kernel network card driver has bugs in that code path (many do) then it will either completely not work at all, or will seem to work for a few days/weeks/months and then start misbehaving.

If I got it right then... Large Segment Offloading activated, if it works correctly with the dom0, will improve network traffic speed over having it disabled. Right?

/Peter


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