Messages in this thread | | | Date | Fri, 22 Jun 2007 10:29:09 +0200 | From | Peter Rabbitson <> | Subject | Re: Terrible IO performance when using 4GB of RAM on a 32 bit machine |
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Robert Hancock wrote: > Peter Rabbitson wrote: >> H. Peter Anvin wrote: >>> >>> 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. >
Ah, it all makes sense now. In this case I assume mem=4000 is perfectly safe and usable for the time being. In the beginning I tried with mem=4g, which obviously did not work. If anyone is interested in adding an exception/workaround for this particular motherboard, I'd be happy to help with testing. I have added more information about the system: current kernel config [1], output of `lspci -vv`[2], dmesg with mem=4000[3].
Thank you!
Peter
[1] http://rabbit.us/pool/4g/config-2.6.21.5.arzamas.6.txt [2] http://rabbit.us/pool/4g/lspci_4000.txt [3] http://rabbit.us/pool/4g/dmesg_4000.txt - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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