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Old 01-08-09, 06:23 PM   #1
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Join Date: Mar 2005
Posts: 81
Default Poor nvidia performance AMD64X2 4GB RAM - 64 IOMMU to blame ?


athlon X2 4600
motherboard : gigabyte GA-M55S-S3
2 X 2GB ram
nvidia 8500 PCI-E
Distro - ubuntu/opensuse amd64

I have recently upgraded my desktop from 1GB ram to 4GB.

Previous i was getting Aperture beyond 4GB messages, I now get

In dmesg it shows:-

Checking aperture...
No AGP bridge found
Node 0: aperture @ 20000000 size 32 MB
Aperture pointing to e820 RAM. Ignoring.
Your BIOS doesn't leave a aperture memory hole
Please enable the IOMMU option in the BIOS setup
This costs you 64 MB of RAM
Mapping aperture over 65536 KB of RAM @ 20000000
PCI: MCFG area at f0000000 reserved in E820
The memory used is not available - i.e i lose 64 MB.

I do not get this in 32bit linux using PAE - i can see all my memory.

After reading around forums I tried iommu=memaper=3 - what excatly does this do ? I noticed that Aperture was set to 256MB with this option - and I lost the 256MB..

What should I set my aperture to ? My gfx card is geforce 8500 256mb PCI-E

I also notice that if I reduce my memory to 2 or 3 GB I do not get that message.

Any sugestions ?
interzoneuk is offline   Reply With Quote