From owner-freebsd-stable@FreeBSD.ORG Mon Oct 8 19:54:54 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 8BDCC16A41A for ; Mon, 8 Oct 2007 19:54:54 +0000 (UTC) (envelope-from jeffk@well.com) Received: from mercury.polycot.com (mercury.polycot.com [70.85.25.84]) by mx1.freebsd.org (Postfix) with SMTP id 61E6113C455 for ; Mon, 8 Oct 2007 19:54:54 +0000 (UTC) (envelope-from jeffk@well.com) Received: (qmail 25272 invoked from network); 8 Oct 2007 19:54:50 -0000 Received: from unknown (HELO ?192.168.0.5?) (70.85.25.93) by mercury.polycot.com with SMTP; 8 Oct 2007 19:54:50 -0000 Mime-Version: 1.0 X-Sender: jeffk@mail.well.com Message-Id: In-Reply-To: References: Date: Mon, 8 Oct 2007 14:54:00 -0500 To: Richard Todd From: Jeff Kramer Content-Type: text/plain; charset="us-ascii" ; format="flowed" 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 19:54:54 -0000 At 2:00 PM -0500 10/8/07, Richard Todd wrote: >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. Sweet, I just downgraded to the 1669 bios rev and it looks like it's running at full speed. I'm compiling an SMP/PAE kernel now, but it looks like this was the fix! Thanks, Richard! -- Jeff Kramer jeffk@well.com http://www.jeffkramer.org/