From owner-freebsd-stable@FreeBSD.ORG Wed May 25 23:03:06 2005 Return-Path: X-Original-To: freebsd-stable@freebsd.org Delivered-To: freebsd-stable@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id EBC9416A41C for ; Wed, 25 May 2005 23:03:06 +0000 (GMT) (envelope-from jd@ugcs.caltech.edu) Received: from riyal.ugcs.caltech.edu (riyal.ugcs.caltech.edu [131.215.176.123]) by mx1.FreeBSD.org (Postfix) with ESMTP id A643743D49 for ; Wed, 25 May 2005 23:03:06 +0000 (GMT) (envelope-from jd@ugcs.caltech.edu) Received: by riyal.ugcs.caltech.edu (Postfix, from userid 3640) id 0653145804; Wed, 25 May 2005 16:03:04 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by riyal.ugcs.caltech.edu (Postfix) with ESMTP id 5E66445802; Wed, 25 May 2005 16:02:58 -0700 (PDT) Date: Wed, 25 May 2005 16:02:58 -0700 (PDT) From: Jon Dama To: Kris Kennaway In-Reply-To: <20050525223811.GA58132@xor.obsecurity.org> Message-ID: References: <3248.172.16.0.199.1116876092.squirrel@172.16.0.1> <200505252342.01938.freebsd.nospam@mekanix.dk> <20050525214555.GA41695@xor.obsecurity.org> <200505260014.37054.freebsd.nospam@mekanix.dk> <20050525223811.GA58132@xor.obsecurity.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Bjarne Wichmann Petersen , Mike Jakubik , Matthias Buelow , freebsd-stable@freebsd.org Subject: Re: Performance of 4.x vs 5.x (Re: Lifetime of FreeBSD branches) X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 25 May 2005 23:03:07 -0000 It's different, yes. But the trouble is that you need a controlled interrupt source--i.e., you have to have some concept of when an "event" might have been handled (were it not for such and such activity). I posit that without that counterfactual talking about PREEMPTION is meaningless. The technique I mentioned--measuring and comparing the jitter was intended to quash measuring the performance of the network stack itself. Do you have an idea how you can pose that counterfactual in a synthetic arrangement more closely connected with the problem at hand? ... -Jon On Wed, 25 May 2005, Kris Kennaway wrote: > On Wed, May 25, 2005 at 03:33:39PM -0700, Jon Dama wrote: > > Could this be quantified by setting up a synthetic experiement: > > > > 1) one machine uses dummynet to generate a uniform packet/sec stream > > 2) another machine has a process receiving those packets and recording > > their arrival relative to the local TSC. afaik, the TSC is the only > > source of wall-time that doesn't involve a system call. Is that right? > > Are the TSCs synchronized on SMP systems? > > 3) Generate another source of activity on the receiving machine to > > estimate the effect of PREEMPTION relative to the (lack of) quiescence. > > 4) use the jitter in the TSC deltas to infer the effect of preemption > > That would be attempting to benchmark something entirely different. > > Kris >