Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752689Ab1BWS1T (ORCPT ); Wed, 23 Feb 2011 13:27:19 -0500 Received: from blu0-omc1-s21.blu0.hotmail.com ([65.55.116.32]:34558 "EHLO blu0-omc1-s21.blu0.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751377Ab1BWS1S (ORCPT ); Wed, 23 Feb 2011 13:27:18 -0500 X-Originating-IP: [174.91.193.52] X-Originating-Email: [pdumas9@sympatico.ca] Message-ID: Date: Wed, 23 Feb 2011 13:27:12 -0500 From: Mathieu Desnoyers To: Christoph Lameter CC: Steven Rostedt , Frederic Weisbecker , "Paul E. McKenney" , linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, "Paul E. McKenney" Subject: Re: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq to kthread References: <20110223013917.GA20996@linux.vnet.ibm.com> <1298425183-21265-11-git-send-email-paulmck@linux.vnet.ibm.com> <20110223161645.GA1819@nowhere> <1298479302.7666.94.camel@gandalf.stny.rr.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.27.31-grsec (i686) X-Uptime: 13:26:49 up 322 days, 4:16, 6 users, load average: 1.70, 2.01, 1.89 User-Agent: Mutt/1.5.18 (2008-05-17) X-OriginalArrivalTime: 23 Feb 2011 18:27:16.0808 (UTC) FILETIME=[4C85E480:01CBD387] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1558 Lines: 55 * Christoph Lameter (cl@linux.com) wrote: > On Wed, 23 Feb 2011, Mathieu Desnoyers wrote: > > > > > > + > > > > > + local_irq_save(flags); > > > > > + cpu = smp_processor_id(); > > Drop this line. > > > > > > + if (per_cpu(rcu_cpu_kthread_task, cpu) == NULL) { > > use this_cpu_read(rcu_cpu_kthread_task) > > > > > > + local_irq_restore(flags); > > > > > + return; > > > > > + } > > > > > + per_cpu(rcu_cpu_has_work, cpu) = 1; > > this_cpu_write(rcu_cpu_has_work, 1); > > > This is not quite true on x86_64 and s390 anymore. __get_cpu_var() now > > uses a segment selector override to get the local CPU variable on x86. > > See x86's percpu.h for details. > > __get_cpu_var cannot use a segment override since there are places where > the address of the variable is taken. One needs to use this_cpu_ops for > that. Ah, thanks for the clarification :) > > > > > True, but we could also argue that the multiple checks for being preempt > > > can also be an issue. > > > > At least on x86 preemption don't actually need to be disabled: selection > > of the right per-cpu memory location is done atomically with the rest of > > the instruction by the segment selector. > > Right. Thanks, Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- 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/