From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757237Ab2CLUZy (ORCPT ); Mon, 12 Mar 2012 16:25:54 -0400 Received: from casper.infradead.org ([85.118.1.10]:51174 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756661Ab2CLUZw convert rfc822-to-8bit (ORCPT ); Mon, 12 Mar 2012 16:25:52 -0400 Message-ID: <1331583916.18960.56.camel@twins> Subject: Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call_srcu() From: Peter Zijlstra To: paulmck@linux.vnet.ibm.com Cc: Lai Jiangshan , Lai Jiangshan , 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, tj@kernel.org Date: Mon, 12 Mar 2012 21:25:16 +0100 In-Reply-To: <20120312183203.GH2471@linux.vnet.ibm.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> <1331032571.11248.277.camel@twins> <1331048093.11248.317.camel@twins> <20120308195825.GC2412@linux.vnet.ibm.com> <1331374193.18960.13.camel@twins> <20120312175432.GF2471@linux.vnet.ibm.com> <1331575097.18960.40.camel@twins> <20120312183203.GH2471@linux.vnet.ibm.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 Mon, 2012-03-12 at 11:32 -0700, Paul E. McKenney wrote: > And another question I should have asked to begin with... Would each > VMA have its own SRCU domain, or are you thinking in terms of one > SRCU domain for all VMAs globally? The latter, single domain for all objects. > If the latter, that pushes pretty strongly for per-CPU SRCU callback > lists. Agreed. I was under the impression the proposed thing had this, but on looking at it again it does not. Shouldn't be hard to add though. > Which brings up srcu_barrier() scalability (and yes, I am working > on rcu_barrier() scalability). One way to handle this at least initially > is to have srcu_barrier() avoid enqueueing callbacks on CPUs whose > callback lists are empty. In addition, if the loop over all CPUs is > preemptible, then there should not be much in the way of realtime issues. Why do we have rcu_barrier() and how is it different from synchronize_rcu()?