From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758235AbYDMMwa (ORCPT ); Sun, 13 Apr 2008 08:52:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752107AbYDMMwX (ORCPT ); Sun, 13 Apr 2008 08:52:23 -0400 Received: from palinux.external.hp.com ([192.25.206.14]:33458 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751921AbYDMMwW (ORCPT ); Sun, 13 Apr 2008 08:52:22 -0400 Date: Sun, 13 Apr 2008 06:52:06 -0600 From: Matthew Wilcox To: Ingo Molnar Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Linus Torvalds Subject: Re: [PATCH] Replace completions with semaphores Message-ID: <20080413125205.GP11962@parisc-linux.org> References: <20080411210022.GJ11962@parisc-linux.org> <1208003081.7427.7.camel@twins> <20080413070513.GB19773@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080413070513.GB19773@elte.hu> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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. -- Intel are signing my paycheques ... these opinions are still mine "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step."