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Old 01-22-09, 04:03 PM   #1
interzoneuk
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Default iommu confusion - 64bit 4GB RAM - pcie card - what settings to use ?????

Hi

I am slightly confused regarding the IOMMU settings.

I have 4G RAM - 64bit distro - Pci express card - 8500

I lose some ram due to this:-

"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 know I can control the setting with iommu=memaper=3 - > this gives 256MB

- I don't have a clue what setting this should be - I have a 256MB Card, all i know is that if i increase this setting I lose more ram - does anyone know what a sensible settling is - do I even use this ram ??

Also am I right in thinking I shouldn't use NVreg_RemapLimit as I have a pci-e card ???

Any help would be very welcomed


athlon X2 4600
motherboard : gigabyte GA-M55S-S3
2 X 2GB ram
nvidia 8500 PCI-E
Distro - ubuntu amd64
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Old 01-22-09, 05:04 PM   #2
logan
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Default Re: iommu confusion - 64bit 4GB RAM - pcie card - what settings to use ?????

I think this is usually a BIOS bug. Have you checked for a new version or maybe you could just try to boot with iommu=noaperture?
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Old 01-22-09, 10:59 PM   #3
zander
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Default Re: iommu confusion - 64bit 4GB RAM - pcie card - what settings to use ?????

Your GPU does not require the IOMMU to address memory above 4GB, so the driver won't make use of it; unless other devices in your system require the IOMMU, you can disable it.
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Old 01-23-09, 03:59 AM   #4
bogey
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Default Re: iommu confusion - 64bit 4GB RAM - pcie card - what settings to use ?????

I have GIGABYTE GA-E7AUM-DS2H, with NVIDIA 9400 chipset, 4096MB memory, 512MB reserved for frame buffer (integrated vga). I'm wondering where 460MB of memory disappears, I see only 2951MB.
I contacted gigabyte support, and they told that some PCI devices could reserve that. But shouldn't that be shown as reserved in dmesg readout?

Distribution: Ubuntu 8.10
Kernel: 2.6.27-9-generic x86_64

Code:
dmesg|grep BIOS-e820 | awk ' { n = strtonum("0x" $6) - strtonum("0x" $4) } { t += n } { print $0 " = "  n/(1024*1024) " MB" } END  { print "Total: " t/(1024*1024) " MB" }'

[    0.000000]  BIOS-e820: 0000000000000000 - 000000000009f800 (usable) = 0.623047 MB
[    0.000000]  BIOS-e820: 000000000009f800 - 00000000000a0000 (reserved) = 0.00195312 MB
[    0.000000]  BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved) = 0.0625 MB
[    0.000000]  BIOS-e820: 0000000000100000 - 0000000060000000 (usable) = 1535 MB
[    0.000000]  BIOS-e820: 0000000060000000 - 0000000080000000 (reserved) = 512 MB
[    0.000000]  BIOS-e820: 0000000080000000 - 000000009fef0000 (usable) = 510.938 MB
[    0.000000]  BIOS-e820: 000000009fef0000 - 000000009fef3000 (ACPI NVS) = 0.0117188 MB
[    0.000000]  BIOS-e820: 000000009fef3000 - 000000009ff00000 (ACPI data) = 0.0507812 MB
[    0.000000]  BIOS-e820: 00000000e0000000 - 00000000e2000000 (reserved) = 32 MB
[    0.000000]  BIOS-e820: 00000000fec00000 - 0000000100000000 (reserved) = 20 MB
[    0.000000]  BIOS-e820: 0000000100000000 - 0000000140000000 (usable) = 1024 MB

Total (reserved + usable): 3634.69 MB
Total usable = 3070.56 MB

# free -m
             total       used       free     shared    buffers     cached
Mem:          2951       2850        101          0        135       2203
-/+ buffers/cache:        511       2440
Swap:         1953          5       1947

# cat /proc/meminfo
MemTotal:      3022292 kB
MemFree:         99316 kB
Buffers:        139044 kB
Cached:        2260860 kB
SwapCached:         84 kB
Active:        1632988 kB
Inactive:      1009592 kB
SwapTotal:     2000052 kB
SwapFree:      1994668 kB
Dirty:               4 kB
Writeback:           0 kB
AnonPages:      242640 kB
Mapped:          65724 kB
Slab:           189248 kB
SReclaimable:   143472 kB
SUnreclaim:      45776 kB
PageTables:      16132 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
WritebackTmp:        0 kB
CommitLimit:   3511196 kB
Committed_AS:   829764 kB
VmallocTotal: 34359738367 kB
VmallocUsed:     89000 kB
VmallocChunk: 34359632891 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
HugePages_Surp:      0
Hugepagesize:     2048 kB
DirectMap4k:   1766336 kB
DirectMap2M:   1902592 kB
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Old 01-23-09, 09:00 AM   #5
apaige
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Default Re: iommu confusion - 64bit 4GB RAM - pcie card - what settings to use ?????

Careful before booting with iommu=off: I couldn't use any of my USB drives with that parameter in the kernel command line. YMMV?
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