On Mon, 13 Apr 2009, Stephen Hemminger wrote:

quoted text
> This is an alternative version of ip/ip6/arp tables locking using
> per-cpu locks.  This avoids the overhead of synchronize_net() during
> update but still removes the expensive rwlock in earlier versions.
>
> The idea for this came from an earlier version done by Eric Duzamet.
> Locking is done per-cpu, the fast path locks on the current cpu
> and updates counters.  The slow case involves acquiring the locks on
> all cpu's.

Doesn't spin_lock() result in a pipeline flush on x86?

iirc there was a benchmark in an RCU paper that tested using per cpu 
spin_locks and the result was that it didn't scale well at all.

/Martin
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