Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932079AbWH1Uqf (ORCPT ); Mon, 28 Aug 2006 16:46:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932083AbWH1Uqf (ORCPT ); Mon, 28 Aug 2006 16:46:35 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:50585 "EHLO pentafluge.infradead.org") by vger.kernel.org with ESMTP id S932079AbWH1Uqf (ORCPT ); Mon, 28 Aug 2006 16:46:35 -0400 Date: Mon, 28 Aug 2006 21:46:11 +0100 From: Christoph Hellwig To: Dipankar Sarma Cc: linux-kernel@vger.kernel.org, Andrew Morton , Ingo Molnar , Paul E McKenney Subject: Re: [PATCH 3/4] RCU: preemptible RCU implementation Message-ID: <20060828204611.GB719@infradead.org> Mail-Followup-To: Christoph Hellwig , Dipankar Sarma , linux-kernel@vger.kernel.org, Andrew Morton , Ingo Molnar , Paul E McKenney References: <20060828160845.GB3325@in.ibm.com> <20060828161222.GE3325@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060828161222.GE3325@in.ibm.com> User-Agent: Mutt/1.4.2.1i X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1645 Lines: 35 On Mon, Aug 28, 2006 at 09:42:22PM +0530, Dipankar Sarma wrote: > From: Paul McKenney > > 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. NACK. While a readers can sleep rcu version definitly has it's we should make it all or nothing. Either we always gurantee that a rcu reader can sleep or never without external patches. Having this a config option is the ultimate defeat for any kind of bug reproducabilility. Please make the patch undconditional and see if it doesn't cause any significant slowdowns in production-like scenaries and then we can switch over to the readers can sleep variant unconditionally at some point. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/