Re: [PATCH 3/4 RFC] RCU: preemptible RCU

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Tue, 2007-08-07 at 11:48 -0700, Paul E. McKenney wrote:
> This patch implements a new version of RCU which allows its read-side
> critical sections to be preempted. It uses a set of counter pairs
> to keep track of the read-side critical sections and flips them
> when all tasks exit read-side critical section. The details
> of this implementation can be found in this paper -
> 
> http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf
> 
> This patch was developed as a part of the -rt kernel development and
> meant to provide better latencies when read-side critical sections of
> RCU don't disable preemption.  As a consequence of keeping track of RCU
> readers, the readers have a slight overhead (optimizations in the paper).
> This implementation co-exists with the "classic" RCU implementations
> and can be switched to at compiler.
> 
> Also includes RCU tracing summarized in debugfs and RCU_SOFTIRQ for
> the preemptible variant of RCU.

Whickedly complex but very cool stuff!

Unfortunately I have nothing to contribute other than praise at the
complex yet elegant way you dodged the need for synchronisation.