From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH 3/4 RFC] RCU: preemptible RCU Date: Wed, 8 Aug 2007 06:09:20 -0700 Message-ID: <20070808130920.GC5024@linux.vnet.ibm.com> References: <20070807183946.GA32110@linux.vnet.ibm.com> <20070807184812.GC10068@linux.vnet.ibm.com> <46B98888.6030600@free.fr> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-rt-users@vger.kernel.org To: John Sigler Return-path: Received: from e3.ny.us.ibm.com ([32.97.182.143]:54034 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754940AbXHHNJX (ORCPT ); Wed, 8 Aug 2007 09:09:23 -0400 Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by e3.ny.us.ibm.com (8.13.8/8.13.8) with ESMTP id l78C4d6I013404 for ; Wed, 8 Aug 2007 08:04:39 -0400 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v8.4) with ESMTP id l78D9MGZ448142 for ; Wed, 8 Aug 2007 09:09:22 -0400 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id l78D9MHf010644 for ; Wed, 8 Aug 2007 09:09:22 -0400 Content-Disposition: inline In-Reply-To: <46B98888.6030600@free.fr> Sender: linux-rt-users-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org On Wed, Aug 08, 2007 at 11:10:32AM +0200, John Sigler wrote: > [ Recipients list trimmed ] > > Paul E. McKenney wrote: > > >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. > > I cannot parse the last sentence :-) Oops... :-/ > Did you mean that this new implementation can be chosen (over the > classic implementation) at compile-time? Yes, via config variables. CONFIG_CLASSIC_RCU selects the "classic" RCU implementation, and CONFIG_PREEMPT_RCU selects the preemptible RCU. CONFIG_PREEMPT_CPU depends on CONFIG_PREEMPT, so that you only are permitted to specify CONFIG_PREEMPT_RT in preemptible kernels. Thanx, Paul