Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750712AbWAITPG (ORCPT ); Mon, 9 Jan 2006 14:15:06 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750715AbWAITPF (ORCPT ); Mon, 9 Jan 2006 14:15:05 -0500 Received: from mail.tv-sign.ru ([213.234.233.51]:9153 "EHLO several.ru") by vger.kernel.org with ESMTP id S1750712AbWAITPE (ORCPT ); Mon, 9 Jan 2006 14:15:04 -0500 Message-ID: <43C2C818.65238C30@tv-sign.ru> Date: Mon, 09 Jan 2006 23:31:20 +0300 From: Oleg Nesterov X-Mailer: Mozilla 4.76 [en] (X11; U; Linux 2.2.20 i686) X-Accept-Language: en MIME-Version: 1.0 To: paulmck@us.ibm.com Cc: linux-kernel@vger.kernel.org, Dipankar Sarma , Manfred Spraul , Linus Torvalds , Andrew Morton Subject: Re: [PATCH 2/5] rcu: don't check ->donelist in __rcu_pending() References: <43C165BC.F7C6DCF5@tv-sign.ru> <20060109185944.GB15083@us.ibm.com> Content-Type: text/plain; charset=koi8-r Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1710 Lines: 44 "Paul E. McKenney" wrote: > > On Sun, Jan 08, 2006 at 10:19:24PM +0300, Oleg Nesterov wrote: > > ->donelist becomes != NULL only in rcu_process_callbacks(). > > > > rcu_process_callbacks() always calls rcu_do_batch() when > > ->donelist != NULL. > > > > rcu_do_batch() schedules rcu_process_callbacks() again if > > ->donelist was not flushed entirely. > > > > So ->donelist != NULL means that rcu_tasklet is either > > TASKLET_STATE_SCHED or TASKLET_STATE_RUN, we don't need to > > check it in __rcu_pending(). > > As Vatsa noted, this is needed if the CPU-hotplug case moves > from ->donelist to ->donelist. It could be omitted if CPU-hotplug > instead moves from ->donelist to ->nextlist, as is the case in Oleg's > patch. The extra grace-period delay should not be a problem for the > presumably rare hotplug case, but: Just to be sure. So do you agree that CPU-hotplug is buggy now (without that patch) ? > o the extra test in __rcu_pending() should be quite inexpensive, > since the cacheline is already loaded given the earlier tests. Yes, it was a cleanup, not an optimization. > o although tasklet_schedule() looks to be perfectly reliable > right now, and although any bugs in tasklet_schedule() must > be fixed, having RCU leakage be the major symptom of > tasklet_schedule() failure sounds quite unfriendly to me. > > So I am not (yet) convinced that this patch is the way to go. Ok, I agree. Oleg. - 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/