Date: Mon, 08 Oct 2007 14:00:34 -0500 From: Richard Todd <rmtodd@ichotolot.servalan.com> To: Jeff Kramer <jeffk@well.com> Cc: freebsd-stable@freebsd.org Subject: Re: PAE Slowdown Message-ID: <x7bqb9a0tp.fsf@ichotolot.servalan.com> In-Reply-To: <servalan.mailinglist.fbsd-stable/p06002004c33006420f72@[192.168.0.5]> (Jeff Kramer's message of "Mon, 8 Oct 2007 11:23:24 -0500") References: <p06002004c33006420f72@[192.168.0.5]>
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Jeff Kramer <jeffk@well.com> 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: <INTEL DP965LT > 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.help
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