Freebsd IP Forwarding performance (question,
and some info) [7-stable, current, em, smp]
kris at FreeBSD.org
Mon Jul 7 11:32:01 UTC 2008
Andre Oppermann wrote:
> 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.
Actually contention from route locking is a major bottleneck even on
packet generation from multiple CPUs on a single host. It is becoming
increasingly necessary that someone look into fixing this.
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