From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753004Ab2ABNbU (ORCPT ); Mon, 2 Jan 2012 08:31:20 -0500 Received: from mx1.redhat.com ([209.132.183.28]:32368 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752606Ab2ABNbR (ORCPT ); Mon, 2 Jan 2012 08:31:17 -0500 Message-ID: <4F01B187.7060008@redhat.com> Date: Mon, 02 Jan 2012 15:30:47 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111115 Thunderbird/8.0 MIME-Version: 1.0 To: Gilad Ben-Yossef CC: Pekka Enberg , linux-kernel@vger.kernel.org, Chris Metcalf , Peter Zijlstra , Frederic Weisbecker , Russell King , linux-mm@kvack.org, Matt Mackall , Sasha Levin , Rik van Riel , Andi Kleen , apkm@linux-foundation.org Subject: Re: [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush References: <1321960128-15191-1-git-send-email-gilad@benyossef.com> <1321960128-15191-5-git-send-email-gilad@benyossef.com> <4F00547A.9090204@redhat.com> <4F008ECA.5040703@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/02/2012 01:59 PM, Gilad Ben-Yossef wrote: > On Sun, Jan 1, 2012 at 6:50 PM, Avi Kivity wrote: > > On 01/01/2012 06:12 PM, Gilad Ben-Yossef wrote: > >> > > >> > Since this seems to be a common pattern, how about: > >> > > >> > zalloc_cpumask_var_or_all_online_cpus(&cpus, GFTP_ATOMIC); > >> > ... > >> > free_cpumask_var(cpus); > >> > > >> > The long-named function at the top of the block either returns a newly > >> > allocated zeroed cpumask, or a static cpumask with all online cpus set. > >> > The code in the middle is only allowed to set bits in the cpumask > >> > (should be the common usage). free_cpumask_var() needs to check whether > >> > the freed object is the static variable. > >> > >> Thanks for the feedback and advice! I totally agree the repeating > >> pattern needs abstracting. > >> > >> I ended up chosing to try a different abstraction though - basically a wrapper > >> on_each_cpu_cond that gets a predicate function to run per CPU to > >> build the mask > >> to send the IPI to. It seems cleaner to me not having to mess with > >> free_cpumask_var > >> and it abstracts more of the general pattern. > >> > > > > This converts the algorithm to O(NR_CPUS) from a potentially lower > > complexity algorithm. Also, the existing algorithm may not like to be > > driven by cpu number. Both are true for kvm. > > > > Right, I was only thinking on my own uses, which are O(NR_CPUS) by nature. > > I wonder if it would be better to create a safe_cpumask_var type with > its own alloc function > free and and sset_cpu function but no clear_cpu function so that the > compiler will catch > cases of trying to clear bits off of such a cpumask? > > It seems safer and also makes handling the free function easier. > > Does that makes sense or am I over engineering it? :-) It makes sense. Depends on the number of call sites, really. If there are several, consolidation helps, also makes it easier to further refactor. -- error compiling committee.c: too many arguments to function