Path: csiph.com!aioe.org!goblin3!goblin.stu.neva.ru!news-2.dfn.de!news.dfn.de!storethat.news.telefonica.de!telefonica.de!news.panservice.it!bofh.it!news.nic.it!robomod From: Thomas Gleixner Newsgroups: linux.kernel Subject: Re: [patch 2/7] timer: Remove FIFO guarantee Date: Tue, 09 Jun 2015 10:10:03 +0200 Message-ID: References: X-Original-To: George Spelvin User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 36 Organization: linux.* mail to news gateway X-Original-Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, viresh.kumar@linaro.org X-Original-Date: Tue, 9 Jun 2015 10:05:56 +0200 (CEST) X-Original-Message-ID: X-Original-References: <20150609053930.25020.qmail@ns.horizon.com> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: aioe.org linux.kernel:1161116 On Tue, 9 Jun 2015, George Spelvin wrote: > Thomas Gleixner wrote: > > > After thinking more about it, I'm even more sure that any code which > > relies on the FIFO "guarantee" is broken today. > > Indeed, I am completely convinced. All I might request is a reassignment > of blame in the commit message. Will do. Thanks for spotting it! > Thank you for your comments on my other blue-sky ideas, too. > > I need to look into why we're using wheels, and what the point is. > How much of an advantage do they have over an efficient priority queue > like a pairing heap? The only reason is performance. The wheel has O(1) insertion and deletion time while heaps and trees usually have O(log(n)). Timer wheel timers are usually timeouts and 99% of them are canceled before expiry. Networking is probably the heaviest use case followed by disk I/O. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/