Date: Mon, 8 Oct 2007 14:54:00 -0500 From: Jeff Kramer <jeffk@well.com> To: Richard Todd <rmtodd@ichotolot.servalan.com> Cc: freebsd-stable@freebsd.org Subject: Re: PAE Slowdown Message-ID: <p0600200cc3303b1f735d@[192.168.0.5]> In-Reply-To: <x7bqb9a0tp.fsf@ichotolot.servalan.com> References: <p06002004c33006420f72@[192.168.0.5]> <x7bqb9a0tp.fsf@ichotolot.servalan.com>
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At 2:00 PM -0500 10/8/07, Richard Todd wrote: >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. 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/
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