From owner-freebsd-stable@FreeBSD.ORG Mon Oct 8 19:45:12 2007 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 7723916A419 for ; Mon, 8 Oct 2007 19:45:12 +0000 (UTC) (envelope-from rmtodd@ichotolot.servalan.com) Received: from mx2.synetsystems.com (mx2.synetsystems.com [76.10.206.15]) by mx1.freebsd.org (Postfix) with ESMTP id 5C85D13C448 for ; Mon, 8 Oct 2007 19:45:11 +0000 (UTC) (envelope-from rmtodd@ichotolot.servalan.com) Received: by mx2.synetsystems.com (Postfix, from userid 66) id 476505A6; Mon, 8 Oct 2007 15:15:18 -0400 (EDT) Received: from rmtodd by servalan.servalan.com with local (Exim 4.66 (FreeBSD)) (envelope-from ) id 1IexqE-000PMG-SU; Mon, 08 Oct 2007 14:00:34 -0500 To: Jeff Kramer References: From: Richard Todd Date: Mon, 08 Oct 2007 14:00:34 -0500 In-Reply-To: (Jeff Kramer's message of "Mon, 8 Oct 2007 11:23:24 -0500") Message-ID: User-Agent: Gnus/5.1008 (Gnus v5.10.8) XEmacs/21.4.20 (berkeley-unix) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: freebsd-stable@freebsd.org Subject: Re: PAE Slowdown 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: Mon, 08 Oct 2007 19:45:12 -0000 Jeff Kramer writes: > Hey all, > > I know that AMD64's the preferred way to run >4 gig systems, but I'm > having a weird situation with 6.2-RELEASE-p8 and 6-STABLE as of last > night. When I compile the PAE kernel, my system performance drops > like a rock. It still boots and everything still runs, but for > instance, running the Flops port my megaflops drop from the 950 MFLOPS > range to 4 MFLOPS. It feels about as fast as a 486. This may not be a PAE-related problem. I say this because I noticed you have the same MB I have: > ACPI APIC Table: Several Intel MBs, including the DP965LT, have a BIOS bug that rears its head when you have 4G (or more) of memory installed, where the BIOS sets the cache control registers incorrectly. This cause a chunk of your main memory (on my system, the chunk between 448MB and 512MB) to be labeled uncachable, with the result being random slowdowns whenever the kernel or user processes happen to touch memory in that chunk. This problem drove me crazy trying to figure out what the problem was until I stumbled on this report on a Linux users' forum explaining the situation. http://forums.fedoraforum.org/showthread.php?t=157232 Fortunately, the workaround is fairly straightforward, adding an rc.d script to twiddle the MTRRs. Assuming this is your problem, if you could post the output of "memcontrol list" it should be possible to id which of the entires is bogus and needs to be removed.