From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030432Ab2CFLwt (ORCPT ); Tue, 6 Mar 2012 06:52:49 -0500 Received: from casper.infradead.org ([85.118.1.10]:40872 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030394Ab2CFLws convert rfc822-to-8bit (ORCPT ); Tue, 6 Mar 2012 06:52:48 -0500 Message-ID: <1331034734.11248.287.camel@twins> Subject: Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call_srcu() From: Peter Zijlstra To: Lai Jiangshan Cc: "Paul E. McKenney" , linux-kernel@vger.kernel.org, mingo@elte.hu, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, patches@linaro.org Date: Tue, 06 Mar 2012 12:52:14 +0100 In-Reply-To: <1331027858-7648-5-git-send-email-laijs@cn.fujitsu.com> References: <1331023359-6987-1-git-send-email-laijs@cn.fujitsu.com> <1331027858-7648-1-git-send-email-laijs@cn.fujitsu.com> <1331027858-7648-5-git-send-email-laijs@cn.fujitsu.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2012-03-06 at 17:57 +0800, Lai Jiangshan wrote: > +void srcu_barrier(struct srcu_struct *sp) > +{ > + struct srcu_sync sync; > + struct srcu_head *head = &sync.head; > + unsigned long chck_seq; /* snap */ > + > + int idle_loop = 0; > + int cpu; > + struct srcu_cpu_struct *scp; > + > + spin_lock_irq(&sp->gp_lock); > + chck_seq = sp->chck_seq; > + for_each_possible_cpu(cpu) { ARGH!! this is really not ok.. so we spend all this time killing srcu_sync_expidited and co because they prod at all cpus for no good reason, and what do you do? Also, what happens if your cpu isn't actually online? > + scp = per_cpu_ptr(sp->srcu_per_cpu, cpu); > + if (scp->head && !safe_less_than(chck_seq, scp->head->chck_seq, > + sp->chck_seq)) { > + /* this path is likely enterred only once */ > + init_completion(&sync.completion); > + srcu_queue_callback(sp, scp, head, > + __synchronize_srcu_callback); > + /* don't need to wakeup the woken state machine */ > + spin_unlock_irq(&sp->gp_lock); > + wait_for_completion(&sync.completion); > + spin_lock_irq(&sp->gp_lock); > + } else { > + if ((++idle_loop & 0xF) == 0) { > + spin_unlock_irq(&sp->gp_lock); > + udelay(1); > + spin_lock_irq(&sp->gp_lock); > + } The purpose of this bit isn't quite clear to me, is this simply a lock break? > + } > + } > + spin_unlock_irq(&sp->gp_lock); > + > + flush_workqueue(srcu_callback_wq); Since you already waited for the completions one by one, what's the purpose of this? > +} > +EXPORT_SYMBOL_GPL(srcu_barrier);