From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753990AbYKHSlS (ORCPT ); Sat, 8 Nov 2008 13:41:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751056AbYKHSlA (ORCPT ); Sat, 8 Nov 2008 13:41:00 -0500 Received: from casper.infradead.org ([85.118.1.10]:54020 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751080AbYKHSlA (ORCPT ); Sat, 8 Nov 2008 13:41:00 -0500 Date: Sat, 8 Nov 2008 10:41:16 -0800 From: Arjan van de Ven To: Linus Torvalds Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Andrew Morton , Peter Zijlstra , Mike Galbraith Subject: Re: [git pull] scheduler updates Message-ID: <20081108104116.48bd26e6@infradead.org> In-Reply-To: References: <20081108170224.GA553@elte.hu> Organization: Intel X-Mailer: Claws Mail 3.6.0 (GTK+ 2.14.4; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 8 Nov 2008 10:28:21 -0800 (PST) Linus Torvalds wrote: > > > On Sat, 8 Nov 2008, Ingo Molnar wrote: > > > > Ingo Molnar (2): > > sched: improve sched_clock() performance > > sched: optimize sched_clock() a bit > > Btw, why do we do that _idiotic_ rdtsc_barrier() AT ALL? > > No sane user can possibly want it. If you do 'rdtsc', there's nothing > you can do about a few cycles difference due to OoO _anyway_. Adding > barriers is entirely meaningless - it's not going to make the return > value mean anything else. > > Can we please just remove that idiocy? Or can somebody give a _sane_ > argument for it? historically it was for early AMD cpus (K7, not sure if early K8 did this) where 2 consecutive rdtsc's in the same codestream would get reordered compared to eachother, so you could observe the tsc go backwards... -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org