Re: [Xen-devel] what's maximum speed setting for xen network?

[Nivedita Singhvi <nsnix@xxxxxxxxxxx>]

Keir Fraser wrote:
> On 22 Apr 2005, at 20:53, mukesh agrawal wrote:
>
> > I've got a configuration with DomU talking to Dom0 over a vif, and 
> > seem to be seeing UDP losses, even at low data rates. (I haven't dug 
> > into this deeply to very the problem yet, though.) So I'd be 
> > interested if you're seeing something similar.
>
> We have no back-pressure / flow control on inter-domain networking. This 
> leads to embarrassing performance for UDP when the sender and receiver 
> share a CPU. The sender fills the receiver's buffers but continues to 
> send even though he drops further packets (no buffer space at receiver) 
> -- then the receiver gets a time slice, receives a ring's worth of 
> packets -- then the sender gets to run for another time slice, most of 
> which again is wasted -- and so on.
> We need a sensible mechanism for ensuring batched packet delivery, but 
> also to ensure that comms rings do not so easily get overflowed. This 
> would vastly improve the inter-domain performance, far more than 
> striving for zero copy or other such tweaks.
> It would be great if someone else is interested in investigating this. :-)
Hi Keir,

Yep, I'm one of the people at least looking into this, don't know
if others are too :). Thrown some instrumentation in and doing some
testing as we speak. Really needed some profiling so was trying to
get the oprofile stuff to work in unstable. From what I saw from
his last post, Jose is working on it.

A few people have kindly agreed to do some testing for me too.

We'll throw some stuff out on the list after the weekend.  I am
tracking all the reports of poor networking performance so if
people do see some issues please continue to post on the list..

thanks,
Nivedita


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