From owner-freebsd-current@FreeBSD.ORG Mon Feb 9 12:46:36 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 726F216A4CF for ; Mon, 9 Feb 2004 12:46:36 -0800 (PST) Received: from mail4.speakeasy.net (mail4.speakeasy.net [216.254.0.204]) by mx1.FreeBSD.org (Postfix) with ESMTP id 4F81543D2F for ; Mon, 9 Feb 2004 12:46:36 -0800 (PST) (envelope-from jhb@FreeBSD.org) Received: (qmail 24126 invoked from network); 9 Feb 2004 20:46:34 -0000 Received: from dsl027-160-063.atl1.dsl.speakeasy.net (HELO server.baldwin.cx) ([216.27.160.63]) (envelope-sender ) encrypted SMTP for ; 9 Feb 2004 20:46:34 -0000 Received: from 10.50.40.205 (gw1.twc.weather.com [216.133.140.1]) by server.baldwin.cx (8.12.10/8.12.10) with ESMTP id i19KjrMA082127; Mon, 9 Feb 2004 15:46:26 -0500 (EST) (envelope-from jhb@FreeBSD.org) From: John Baldwin To: "Poul-Henning Kamp" , David Schultz Date: Mon, 9 Feb 2004 14:55:14 -0500 User-Agent: KMail/1.5.4 References: <16693.1076233792@critter.freebsd.dk> In-Reply-To: <16693.1076233792@critter.freebsd.dk> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200402091455.14961.jhb@FreeBSD.org> X-Spam-Checker-Version: SpamAssassin 2.55 (1.174.2.19-2003-05-19-exp) cc: current@FreeBSD.ORG cc: tjr@FreeBSD.ORG cc: Jun Su Subject: Re: PID Allocator Performance Results (was: Re: [UPDATE] new pid alloc...) X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 09 Feb 2004 20:46:36 -0000 On Sunday 08 February 2004 04:49 am, Poul-Henning Kamp wrote: > In message <20040208094537.GA14749@VARK.homeunix.com>, David Schultz writes: > >> 10nsec per operation is getting you into the territory of effective > >> TSC-timecounter resolution, RAM access time, cache miss delays > >> and all sorts of other hardware effects. > > > >To avoid jitter and timestamping overhead, I read the time only at > >the start and end of the entire sequence of 10000 operations. > >I obtained the sample variance by running the entire test three > >times, i.e. > > Yes, but you have to remember that quite a lot of stuff happens > in the kernel of your iteration, and the stratification seems > to happen there. > > >Nevertheless, you're definitely right about the stratification. > > > >Yes, I realize that. I took 10 more samples of 10000 forks each > >with 5000 sleeping processes in the background and got the > >following: > > > >This data show a difference at the 95% confidence level, namely, > >that the NetBSD algorithm is about 1% faster on a system with 5000 > >processes (and only 0.1% faster if you're looking at the total > >overhead of fork() rather than vfork().) I think that pretty much > >rules out performance as the deciding factor between the two. > > Uhm, if you are using "Student's T" you have to remember that it > is only valid for gaussian noise processes. The stratification > we see is not any where near to gaussian. > > Either way: "tjr" should be our choice. Agreed. I'll defer to das@ on this one as he is the one who has done the actual research. Tom's version certainly seems to be the consensus. -- John Baldwin <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org