Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756996Ab3HLPRq (ORCPT ); Mon, 12 Aug 2013 11:17:46 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:55332 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756228Ab3HLPRp (ORCPT ); Mon, 12 Aug 2013 11:17:45 -0400 Date: Mon, 12 Aug 2013 08:16:18 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Lai Jiangshan , Steven Rostedt , linux-kernel@vger.kernel.org, Dipankar Sarma Subject: Re: [PATCH 5/8] rcu: eliminate deadlock for rcu read site Message-ID: <20130812151618.GR29406@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1375871104-10688-1-git-send-email-laijs@cn.fujitsu.com> <1375871104-10688-6-git-send-email-laijs@cn.fujitsu.com> <20130808204020.GA31127@linux.vnet.ibm.com> <5204B6EF.6000905@cn.fujitsu.com> <20130812135544.GG27162@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130812135544.GG27162@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13081215-7182-0000-0000-0000080DF404 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1270 Lines: 27 On Mon, Aug 12, 2013 at 03:55:44PM +0200, Peter Zijlstra wrote: > On Fri, Aug 09, 2013 at 05:31:27PM +0800, Lai Jiangshan wrote: > > On 08/09/2013 04:40 AM, Paul E. McKenney wrote: > > > One problem here -- it may take quite some time for a set_need_resched() > > > to take effect. This is especially a problem for RCU priority boosting, > > > but can also needlessly delay preemptible-RCU grace periods because > > > local_irq_restore() and friends don't check the TIF_NEED_RESCHED bit. > > > > > > The final effect of deboosting(rt_mutex_unlock()) is also accomplished > > via set_need_resched()/set_tsk_need_resched(). > > set_need_resched() is enough for RCU priority boosting issue here. > > But there's a huge difference between the boosting and deboosting side > of things. rcu_read_unlock_special() starts the boost, the deboosting > only matters if/when you reschedule. Or if there is a pre-existing runnable task whose priority is such that deboosting makes it the highest-priority task. Thanx, Paul -- 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/