linux-kernel - Re: [PATCH 3/4 RFC] RCU: preemptible RCU

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Message-Id: <1186514309.11797.171.camel@lappy>
Date:	Tue, 07 Aug 2007 21:18:29 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	mingo@...e.hu, akpm@...ux-foundation.org, dipankar@...ibm.com,
	josht@...ux.vnet.ibm.com, tytso@...ibm.com, dvhltc@...ibm.com,
	tglx@...utronix.de
Subject: Re: [PATCH 3/4 RFC] RCU: preemptible RCU

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.

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