From mboxrd@z Thu Jan 1 00:00:00 1970 From: Evgeniy Polyakov Subject: Re: [PATCH RFC] v5 expedited "big hammer" RCU grace periods Date: Mon, 18 May 2009 00:02:23 +0400 Message-ID: <20090517200223.GA31029@ioremap.net> References: <20090517191141.GA25915@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, mingo@elte.hu, akpm@linux-foundation.org, torvalds@linux-foundation.org, davem@davemloft.net, dada1@cosmosbay.com, jeff.chua.linux@gmail.com, paulus@samba.org, laijs@cn.fujitsu.com, jengelh@medozas.de, r000n@r000n.net, benh@kernel.crashing.org, mathieu.desnoyers@polymtl.ca To: "Paul E. McKenney" Return-path: Received: from tservice.ru ([195.178.208.66]:40651 "EHLO tservice.net.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754368AbZEQUC1 (ORCPT ); Sun, 17 May 2009 16:02:27 -0400 Content-Disposition: inline In-Reply-To: <20090517191141.GA25915@linux.vnet.ibm.com> Sender: netfilter-devel-owner@vger.kernel.org List-ID: Hi. On Sun, May 17, 2009 at 12:11:41PM -0700, Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > Fifth cut of "big hammer" expedited RCU grace periods. This uses per-CPU > kthreads that are scheduled in parallel by a call to smp_call_function() > by yet another kthread. The synchronize_sched(), synchronize_rcu(), > and synchronize_bh() primitives wake this kthread up and then wait for > it to force the grace period. I'm curious, but doesn't the fact that registered 'barrier' callback is invoked mean grace period completion? I.e. why to bother with rescheduling, waiting for thread to complete and so on, when we only care in the fact that 'barrier' callback is invoked, and thus all previous ones are completed? Or it is done just for the simplicity, since all rescheduling machinery already manages the rcu bits correctly, so you do not want to put it directly into 'barrier' callback? -- Evgeniy Polyakov