Read Copy Update

[Doug Rabson]

So, I was reading the latest installment of the SCO soap on slashdot
today (bizarre - they seem to be claiming that they own all code that
was ever linked to a System V kernel) and I ended up trying to figure
out exactly what this RCU thing is that they claim is infringing their
right to obtain money with menaces.

I read one of the original papers at
http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf and its a
surprisingly simple idea. Basically for certain data structures which
are read-mostly, you can make the entire read path lock-free at the
expense of making updates quite a bit more expensive. They claim that
its much faster than reader-writer locks both for light contention and
for heavy contention.

I imagine that a FreeBSD implementation of RCU wouldn't actually be too
hard and it might be well worth it as an alternative way of managing
concurrency, e.g. for the routing cache and the name cache (and probably
lots of other things).