From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266814AbUGLOTJ (ORCPT ); Mon, 12 Jul 2004 10:19:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266818AbUGLOTJ (ORCPT ); Mon, 12 Jul 2004 10:19:09 -0400 Received: from mx1.elte.hu ([157.181.1.137]:52145 "EHLO mx1.elte.hu") by vger.kernel.org with ESMTP id S266814AbUGLOTG (ORCPT ); Mon, 12 Jul 2004 10:19:06 -0400 Date: Mon, 12 Jul 2004 16:19:12 +0200 From: Ingo Molnar To: Chris Friesen Cc: Con Kolivas , ck kernel mailing list , linux-kernel@vger.kernel.org, Andrew Morton , Arjan van de Ven Subject: Re: [ck] Re: [announce] [patch] Voluntary Kernel Preemption Patch Message-ID: <20040712141912.GA14710@elte.hu> References: <20040711143853.GA6555@elte.hu> <40F29CF9.4000400@nortelnetworks.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <40F29CF9.4000400@nortelnetworks.com> User-Agent: Mutt/1.4.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Chris Friesen wrote: > >it was reporting more accurate latencies, except that there were strange > >spikes of latencies. It turned out that for whatever reason, userspace > >RDTSC is not always reliable on my box (!). > > Would the fact that rdtsc is not serializing have any effect here? Or > would that be a small enough error to not have any effect? even though it's not serializing (to other instructions), one would expect the '64-bit cycle counter' to be fetched atomically. And several milliseconds cannot be explained with any micr-op delays anyway. Ingo