From owner-freebsd-hackers@FreeBSD.ORG Sat Oct 25 12:42:03 2003 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 66F8816A4B3 for ; Sat, 25 Oct 2003 12:42:03 -0700 (PDT) Received: from smtp3.Stanford.EDU (smtp3.Stanford.EDU [171.64.14.172]) by mx1.FreeBSD.org (Postfix) with ESMTP id C477B43F85 for ; Sat, 25 Oct 2003 12:42:02 -0700 (PDT) (envelope-from tedu@stanford.edu) Received: from saga10.Stanford.EDU (saga10.Stanford.EDU [171.64.15.140]) by smtp3.Stanford.EDU (8.12.10/8.12.10) with ESMTP id h9PJfu6U012457; Sat, 25 Oct 2003 12:41:57 -0700 (PDT) Date: Sat, 25 Oct 2003 12:41:56 -0700 (PDT) From: Ted Unangst To: Terry Lambert In-Reply-To: <3F9AC007.DB48DE9D@mindspring.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII cc: freebsd-hackers@freebsd.org cc: Michel TALON Subject: Re: Some mmap observations compared to Linux 2.6/OpenBSD X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 25 Oct 2003 19:42:03 -0000 On Sat, 25 Oct 2003, Terry Lambert wrote: > Why does the benchmark need to be "fixed" for OpenBSD and not > for any other platform? openbsd does not have a unified cache between file system (pread) and vm (mmap) interfaces. in the real world, it's unusual to find an application that uses both interfaces for its data files. a good benchmark at least attempts to model real world application behavior. > My point here is that a benchmark measures what it measures, and > if you don't like what it measures, making it measure something > else is not a fix for the problem that it was originally intended > to show. then the benchmark author should explain what's going on. "touching a cached page" and "touching a page and reading it from disk" are different events. if the name of the graph were "reading an mmaped page after priming the disk cache with pread", then fine. but it's not. i'd like a benchmark to either attempt to accurately model (some slice of) real life or accurately explain what it is measuring. -- "I am clearly more popular than Reagan. I am in my third term. Where's Reagan? Gone after two! Defeated by George Bush and Michael Dukakis no less." - M. Barry, Mayor of Washington, DC