From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760975AbYDNPlz (ORCPT ); Mon, 14 Apr 2008 11:41:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754106AbYDNPls (ORCPT ); Mon, 14 Apr 2008 11:41:48 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:50749 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753647AbYDNPls (ORCPT ); Mon, 14 Apr 2008 11:41:48 -0400 Date: Mon, 14 Apr 2008 17:41:29 +0200 From: Ingo Molnar To: Matthew Wilcox Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Linus Torvalds Subject: Re: [PATCH] Replace completions with semaphores Message-ID: <20080414154129.GB22259@elte.hu> References: <20080411210022.GJ11962@parisc-linux.org> <1208003081.7427.7.camel@twins> <20080413070513.GB19773@elte.hu> <20080413125205.GP11962@parisc-linux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080413125205.GP11962@parisc-linux.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0003] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Matthew Wilcox wrote: > On Sun, Apr 13, 2008 at 09:05:13AM +0200, Ingo Molnar wrote: > > there's also another aspect: completions are faster a bit > > in theory, because they know that they will schedule most of the time - > > while semaphores assume that they will _not_ schedule. (And that's > > exactly because the intent of the developer when using a completion is > > crystal clear.) > > In practice though, the current implementation is slower. [...] any URL to benchmarks? > [...] Of course, that's fixable, and I strongly suspect that the > current users of completions simply don't care about speed -- the > normal use of completions is in startup and shutdown paths where a > millisecond extra isn't going to be noticable. completions and semaphores act in the sub-microsecond range, not in the milliseconds range. Ingo