Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750951AbWI3NSU (ORCPT ); Sat, 30 Sep 2006 09:18:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750965AbWI3NSU (ORCPT ); Sat, 30 Sep 2006 09:18:20 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:23747 "EHLO mx2.mail.elte.hu") by vger.kernel.org with ESMTP id S1750934AbWI3NST (ORCPT ); Sat, 30 Sep 2006 09:18:19 -0400 Date: Sat, 30 Sep 2006 15:09:58 +0200 From: Ingo Molnar To: Dipankar Sarma Cc: Andrew Morton , Thomas Gleixner , "Paul E. McKenney" , LKML , Jim Gettys , John Stultz , David Woodhouse , Arjan van de Ven , Dave Jones Subject: Re: [patch 08/23] dynticks: prepare the RCU code Message-ID: <20060930130958.GA12021@elte.hu> References: <20060929234435.330586000@cruncher.tec.linutronix.de> <20060929234439.721237000@cruncher.tec.linutronix.de> <20060930013641.263a1cc3.akpm@osdl.org> <20060930122514.GC8763@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060930122514.GC8763@in.ibm.com> User-Agent: Mutt/1.4.2.1i X-ELTE-SpamScore: -2.8 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.8 required=5.9 tests=ALL_TRUSTED,AWL,BAYES_50 autolearn=no SpamAssassin version=3.0.3 -3.3 ALL_TRUSTED Did not pass through any untrusted hosts 0.5 BAYES_50 BODY: Bayesian spam probability is 40 to 60% [score: 0.5000] -0.0 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1300 Lines: 29 * Dipankar Sarma wrote: > It is duplicating code. That can be easily fixed, but we need to > figure out what we really want from RCU when we are about to switch > off the ticks. It is hard if you want to finish off all the pending > RCUs and go to nohz state. Can you live with backing out if there are > pending RCUs ? the thing is that when we go idle we /want/ to process whatever delayed work there might be - rate limited or not. Do you agree with that approach? I consider this a performance feature as well: this way we can utilize otherwise lost idle time. It is not a problem that we dont 'batch' this processing: we are really idle and we've got free cycles to burn. We could even do an RCU processing loop that immediately breaks out if need_resched() gets set [by an IRQ or by another CPU]. secondly, i think i saw functionality problems when RCU was not completed before going idle - for example synchronize_rcu() on another CPU would hang. what approach would you suggest to achieve these goals? Ingo - 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/