From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nivedita Singhvi Subject: Re: what's maximum speed setting for xen network? Date: Sat, 23 Apr 2005 10:36:39 -0700 Message-ID: <426A87A7.8010109@comcast.net> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: xen-devel@lists.xensource.com, zhaoxin@eecs.umich.edu, mukesh agrawal List-Id: xen-devel@lists.xenproject.org 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