Blaine Christian wrote:
I did read your comment on BGP lending itself to SMP. Can you
elaborate on where you might have seen this? It has been a pretty
monolithic implementation for as long as I can remember. In fact,
that was why I asked the question, to see if anyone had actually
observed a functioning multi-processor implementation of the BGP
process.
I can make the SMP statement with some authority as I have done the
internal
design of the OpenBGPd RDE and my co-worker Claudio has implemented
it. Given
proper locking of the RIB a number of CPU's can crunch on it and
handle neighbor
communication indepently of each other. If you look at Oracle
databases they
manage to scale performance with factor 1.9-1.97 per CPU. There is
no reason
to believe we can't do this with the BGP 'database'.
Neat! So you were thinking you would leave the actual route selection
process monolithic and create separate processes per peer? I have seen
folks doing something similar with separate MBGP routing instances.
Had not heard of anyone attempting this for a "global" routing table
with separate threads per neighbor (as opposed to per table). What do
you do if you have one neighbor who wants to send you all 2M routes
though? I am thinking of route reflectors specifically but also
confederation EIBGP sessions.
> I think you hit the nail on the head regarding record locking. This is
> the thing that is going to bite you if anything will. I have heard
> none of the usual suspects speak up so I suspect that either this
> thread is now being ignored or no one has heard of an implementation
> like the one you just described.
In BGP there is no 'global' route (actually path) selection in BGP.
Everything is done per prefix+path. In the RIB you can just lock the prefix,
insert the new path and recalculate which one wins. Then issue the update
to the FIB, if any. Work done. Statistically there is very little
contention on the prefix and the path records. For contention two updates
for the same prefix would have to arrive at the same time from two different
peers handled by different CPU's. I'd guess the SMP scaling factor for BGP
is around 1.98. The 0.02 go lost for locking overhead and negative caching
effects. Real serialization happens only at the FIB change queue. However
serializing queues can be handled very efficiently on SMP too.
--
Andre