From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756712AbYAIVCm (ORCPT ); Wed, 9 Jan 2008 16:02:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756021AbYAIVB5 (ORCPT ); Wed, 9 Jan 2008 16:01:57 -0500 Received: from terminus.zytor.com ([198.137.202.10]:44446 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755991AbYAIVB4 (ORCPT ); Wed, 9 Jan 2008 16:01:56 -0500 Message-ID: <47853537.4070702@zytor.com> Date: Wed, 09 Jan 2008 12:57:27 -0800 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: Andi Kleen CC: Arjan van de Ven , Ingo Molnar , tglx@linutronix.de, linux-kernel@vger.kernel.org Subject: Re: More breakage in native_rdtsc out of line in git-x86 References: <20080109035534.GA30321@basil.nowhere.org> <20080109090956.GA14274@elte.hu> <20080109141908.GB12855@one.firstfloor.org> <20080109152208.GA21280@elte.hu> <20080109155124.GB12923@one.firstfloor.org> <20080109163017.GG17739@elte.hu> <20080109174800.GA15346@one.firstfloor.org> <20080109122559.38bc8c33@laptopd505.fenrus.org> <20080109204028.GA15612@one.firstfloor.org> In-Reply-To: <20080109204028.GA15612@one.firstfloor.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andi Kleen wrote: > > People tend to make jokes about optimizing the idle loop too, but they're > actually wrong. Exit latency for the idle loop is important -- it > decides how quickly you can react to load changes on idle CPUs. > > For short udelays I suspect shorter exit latency is also moderately useful. > > But anyways there are plenty of gtod users outside the X server. > > e.g. common not user space case is packet timestamps. > It's also very common to put gtod calls around select and poll, because the standard interface doesn't tell you how long you have been away (Linux at least used to have it, but glibc "fixed" that...) -hpa