From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932454Ab2CIQA5 (ORCPT ); Fri, 9 Mar 2012 11:00:57 -0500 Received: from e8.ny.us.ibm.com ([32.97.182.138]:36433 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932365Ab2CIP7K (ORCPT ); Fri, 9 Mar 2012 10:59:10 -0500 Date: Thu, 8 Mar 2012 11:58:25 -0800 From: "Paul E. McKenney" To: Peter Zijlstra 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 Subject: Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call_srcu() Message-ID: <20120308195825.GC2412@linux.vnet.ibm.com> Reply-To: paulmck@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1331048093.11248.317.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12030915-9360-0000-0000-000004642CA0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 06, 2012 at 04:34:53PM +0100, Peter Zijlstra wrote: > On Tue, 2012-03-06 at 23:12 +0800, Lai Jiangshan wrote: > > On Tue, Mar 6, 2012 at 7:16 PM, Peter Zijlstra wrote: > > > On Tue, 2012-03-06 at 17:57 +0800, Lai Jiangshan wrote: > > >> srcu_head is bigger, it is worth, it provides more ability and simplify > > >> the srcu code. > > > > > > Dubious claim.. memory footprint of various data structures is deemed > > > important. rcu_head is 16 bytes, srcu_head is 32 bytes. I think it would > > > be real nice not to have two different callback structures and not grow > > > them as large. > > > > CC: tj@kernel.org > > It could be better if workqueue also supports 2*sizeof(long) work callbacks. > > That's going to be very painful if at all possible. > > > I prefer ability/functionality a little more, it eases the caller's pain. > > preemptible callbacks also eases the pressure of the whole system. > > But I'm also ok if we limit the srcu-callbacks in softirq. > > You don't have to use softirq, you could run a complete list from a > single worklet. Just keep the single linked rcu_head list and enqueue a > static (per-cpu) worker to process the entire list. I like the idea of SRCU using rcu_head. I am a little concerned about what happens when there are lots of SRCU callbacks, but am willing to wait to solve those problems until the situation arises. But I guess I should ask... Peter, what do you expect the maximum call_srcu() rate to be in your use cases? If tens of thousands are possible, some adjustments will be needed. Thanx, Paul