From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx126.postini.com [74.125.245.126]) by kanga.kvack.org (Postfix) with SMTP id C54D96B005C for ; Mon, 2 Jan 2012 06:59:31 -0500 (EST) Received: by vbbfn1 with SMTP id fn1so16146720vbb.14 for ; Mon, 02 Jan 2012 03:59:30 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <4F008ECA.5040703@redhat.com> 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> Date: Mon, 2 Jan 2012 13:59:30 +0200 Message-ID: Subject: Re: [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush From: Gilad Ben-Yossef Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Avi Kivity 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 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: >> > >> > =A0 zalloc_cpumask_var_or_all_online_cpus(&cpus, GFTP_ATOMIC); >> > =A0 ... >> > =A0 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). =A0free_cpumask_var() needs to check whe= ther >> > 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 w= rapper >> 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. =A0Also, the existing algorithm may not like to be > driven by cpu number. =A0Both 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? :-) Gilad --=20 Gilad Ben-Yossef Chief Coffee Drinker gilad@benyossef.com Israel Cell: +972-52-8260388 US Cell: +1-973-8260388 http://benyossef.com "Unfortunately, cache misses are an equal opportunity pain provider." -- Mike Galbraith, LKML -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org