Freebsd IP Forwarding performance (question, and some info) [7-stable, current, em, smp]

[Andre Oppermann]

Robert Watson wrote:
> Experience suggests that forwarding workloads see significant lock 
> contention in the routing and transmit queue code.  The former needs 
> some kernel hacking to address in order to improve parallelism for 
> routing lookups.  The latter is harder to address given the hardware 
> you're using: modern 10gbps cards frequently offer multiple transmit 
> queues that can be used independently (which our cxgb driver supports), 
> but 1gbps cards generally don't.

Actually the routing code is not contended.  The workload in router
is mostly serialized without much opportunity for contention.  With
many interfaces and any-to-any traffic patterns it may get some
contention.  The locking overhead per packet is always there and has
some impact though.

-- 
Andre