Re: [PATCH] netfilter: use per-cpu spinlock rather than RCU

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On Mon, 13 Apr 2009, Stephen Hemminger wrote:

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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