Re: [Xen-devel] network hang fixed for me

[Steven Hand <Steven.Hand@xxxxxxxxxxxx>]

>Whatever the changes were in the last 24 hours, they appear to have
>fixed all of my network problems. Somewhere recently the problem of 'xm
>destroy' not always destroying a domain was fixed too.
>
>That puts an end to my two biggest annoyances with xen. Woohoo!
>
>Just out of interest, what were the problems causing the network hang?

See cset 1.1315 -- basically the frontend/backend synchronization was
being rather too agreesive at 'batching' (aka holding off sending events 
to avoid taking too many hypercalls). In some circumstances (e.g. IP 
fragments) this could lead to the backend being unable to make any 
progress ('waiting' for the remaining fragments) while the frontend 
would happily fail to notify it of these. 

This only affects you when communicating domU<->dom0 ; for the default
(for us!) case where domU packets are bridged at L2 onto the wire, no
reassembly happens and hence no hang... if people use this configuration
exclusively they can enable the old behaviour (one of the new build 
options), but it's probably not worth it (we see very little performance
effect using the 'pessimistic' strategy all the time). 

A second bug has also just been fixed -- this was actually a linux 
bug, or at least a bug which arose due to linux code assuming something
which is generally true but not guaranteed to be (and in fact, isn't 
true when using xen virtual devices). 

Anyway: hopefully we're now moving closer to stabilising 2.0 beta and 
should be able to do the official 2.0 'release' soon. 


cheers,

S.