From owner-freebsd-current Sun Feb 9 7:28:39 2003 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 B900137B401; Sun, 9 Feb 2003 07:28:38 -0800 (PST) Received: from HAL9000.homeunix.com (12-233-57-224.client.attbi.com [12.233.57.224]) by mx1.FreeBSD.org (Postfix) with ESMTP id 210D443F3F; Sun, 9 Feb 2003 07:28:38 -0800 (PST) (envelope-from dschultz@uclink.berkeley.edu) Received: from HAL9000.homeunix.com (localhost [127.0.0.1]) by HAL9000.homeunix.com (8.12.6/8.12.5) with ESMTP id h19FSaoH002391; Sun, 9 Feb 2003 07:28:36 -0800 (PST) (envelope-from dschultz@uclink.berkeley.edu) Received: (from das@localhost) by HAL9000.homeunix.com (8.12.6/8.12.5/Submit) id h19FSaCH002390; Sun, 9 Feb 2003 07:28:36 -0800 (PST) (envelope-from dschultz@uclink.berkeley.edu) Date: Sun, 9 Feb 2003 07:28:36 -0800 From: David Schultz To: Marcin Dalecki Cc: Adrian Chadd , Terry Lambert , Ray Kohler , freebsd-current@freebsd.org Subject: Re: Compiling with high optimization? Message-ID: <20030209152836.GB1390@HAL9000.homeunix.com> Mail-Followup-To: Marcin Dalecki , Adrian Chadd , Terry Lambert , Ray Kohler , freebsd-current@freebsd.org References: <20030208173756.GA56030@arkadia.nv.cox.net> <20030208232724.GA20435@HAL9000.homeunix.com> <3E459BF3.BB3FC381@mindspring.com> <20030209002542.GA20812@HAL9000.homeunix.com> <20030209141006.GB33928@skywalker.creative.net.au> <20030209150120.GA2263@HAL9000.homeunix.com> <3E4671E6.8090000@gmx.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3E4671E6.8090000@gmx.net> Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Thus spake Marcin Dalecki : > David Schultz wrote: > > >Strangely, gcc in FreeBSD 5.0 actually generates *slower* code > >when compiling for more recent architectures than when compiling > >for a 386. I don't know whether that is a bug in gcc or whether > >gcc is using some fancy feature like SSE that the kernel handles > >poorly on context switches. I think there was some discussion on > >the lists about it earlier. > The reason is that the optimization done by GCC are ill balanced. > All the scheduling of instractions and what a not - which would be > fine on a micro scope level is causing so much higher pressure > on the CPUs caches that the code is actually loosing. Interesting. So they redid the code generation for gcc 3 and their new tricks backfired. But at least they fixed the completely braindead things gcc 2.9x was doing with alignment, floating point, and combinations thereof, and they got the compiler to do more reasonable things on ia64. Any idea when they will have fixed the i386 anti-optimizations? To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message