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Date: Thu, 21 Jun 2007 18:00:00 -0600 From: Robert Hancock <hancockr@...w.ca> To: Peter Rabbitson <rabbit@...bit.us> Cc: "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org Subject: Re: Terrible IO performance when using 4GB of RAM on a 32 bit machine Peter Rabbitson wrote: > H. Peter Anvin wrote: >> Peter Rabbitson wrote: >>> I have captured dmesg output without mem[5], with mem=3900M[6] and >>> mem=2048M[7]. >>> >> >> What does /proc/mtrr look like in the two cases? >> > > Identical for mem=3900 and without it. > > reg00: base=0x00000000 ( 0MB), size=2048MB: write-back, count=1 > reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1 > reg02: base=0xc0000000 (3072MB), size= 512MB: write-back, count=1 > reg03: base=0xe0000000 (3584MB), size= 256MB: write-back, count=1 > reg04: base=0xf0000000 (3840MB), size= 128MB: write-back, count=1 > reg05: base=0xf8000000 (3968MB), size= 32MB: write-back, count=1 Looks like another case of bad MTRRs on an Intel motherboard? The BIOS is marking only memory up to 4000MB as cacheable, but the actual memory extends up to about 4031MB. Therefore anything that accesses the top 31MB of memory will run very slow. -- Robert Hancock Saskatoon, SK, Canada To email, remove "nospam" from hancockr@...pamshaw.ca Home Page: http://www.roberthancock.com/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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