512 MB memory hole in Fujitsu-Siemens Celsius V810

  • Thread starter Thread starter Rui Pedro Mendes Salgueiro
  • Start date Start date
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Rui Pedro Mendes Salgueiro

Hello


Recently our department bought a Fujitsu-Siemens Celsius V810 with
4 GB memory. This has two Opterons processors and a D1692 motherboard,
similar to a Tyan Thunder K8W (S2885). The BIOS version is 1.04.1692
(2004/06/22).

The computer only shows 3.5 GB (this is both in the BIOS, the OS
(Suse Linux 9.1) and memtest plus, although they all probably are
receiving the information from the BIOS.

I discovered that this is due to a setting in the BIOS setup menus:
menu "Advanced"
menu "Chipset"
4GB Memory Hole Adjust [Auto]
4GB Memory Hole Size [512 MB]

the BIOS help says:

[Auto]
Adjust the memory hole size automatically according to the
memory space used by PCI devices.

I tried to reduce manually the size of the memory hole, but it seems
that the BIOS overrides it again to 512 MB.

I can understand that there is need to reserve this memory hole,
but what I find strange is that the motherboard is unable to move
those 512 MB to some address above 4 GB. Another department bought
a similar computer, but with 8 GB, of which they can use only 7.5 GB

I haven't seen that computer, so I don't know which addresses are
being used but I guess that they are not continuous and the OS is
able to deal with that. After all, OSs for PCs have had to do deal
with memory holes ever since the 286 and computers with more than
1 MB appeared.

I would expect to be possible to remap some of the memory above 4 GB
so as to not collide with the memory hole. But it doesn't do that
automatically and I haven't found such a setting on the BIOS setup.

Anyone knows if there is some way to use those 512 MB ?


I have just found a message in a mailing list archive:

http://www.clustermatic.org/pipermail/linuxbios/2004-January/006372.html

I have an Opteron machine based on the Tyan K8W S2885
mainboard which is equipped with 8GB of RAM (8x1GB DIMM).
The BIOS is mapping the PCI/AGP devices into the address
space immediately below 4GB and so consequently, I am losing
access to nearly an entire 1GB of RAM. I've spoken to Tyan
about this and they acknowledged that it it is principle
possible for the BIOS to remap the DIMM presently located
at 3GB to 9GB but that they have no intention of including
this option in their BIOS as it "penalizes 32-bit OS's that
cannot use more than 4GB."

Bogus excuse, BTW. If the BIOS had an option to chose either 32-bit
or 64-bit OS, each user could chose the configuration that suits
him best. BTW, I don't remember if the 32 bit mode of the AMD 64
is compatible with the 36-bit segmented mode of the Xeon (not sure
if the Pentiums also have that) ?

I read something similar at:
http://www.spinics.net/lists/amd64/msg00321.html

This seems to mean that there is not much hope, but OTOH, this
message is some months old. Maybe things have changed ?

Thanks in advance
 
Hello


Recently our department bought a Fujitsu-Siemens Celsius V810 with
4 GB memory. This has two Opterons processors and a D1692 motherboard,
similar to a Tyan Thunder K8W (S2885). The BIOS version is 1.04.1692
(2004/06/22).

The computer only shows 3.5 GB (this is both in the BIOS, the OS
(Suse Linux 9.1) and memtest plus, although they all probably are
receiving the information from the BIOS.

I discovered that this is due to a setting in the BIOS setup menus:
menu "Advanced"
menu "Chipset"
4GB Memory Hole Adjust [Auto]
4GB Memory Hole Size [512 MB]

the BIOS help says:

[Auto]
Adjust the memory hole size automatically according to the
memory space used by PCI devices.

I tried to reduce manually the size of the memory hole, but it seems
that the BIOS overrides it again to 512 MB.
Click to expand...

This just came up in a discussion in another thread and I voiced my concern
that we might be going through yet another hardware transition which would
bring new legacy baggage... IOW this hole just below the 4GB mark.
I can understand that there is need to reserve this memory hole,
but what I find strange is that the motherboard is unable to move
those 512 MB to some address above 4 GB. Another department bought
a similar computer, but with 8 GB, of which they can use only 7.5 GB

I haven't seen that computer, so I don't know which addresses are
being used but I guess that they are not continuous and the OS is
able to deal with that. After all, OSs for PCs have had to do deal
with memory holes ever since the 286 and computers with more than
1 MB appeared.

I would expect to be possible to remap some of the memory above 4 GB
so as to not collide with the memory hole. But it doesn't do that
automatically and I haven't found such a setting on the BIOS setup.

Anyone knows if there is some way to use those 512 MB ?
Click to expand...

I recall a trick from the 486 computers which had a similar hole just below
16MB and would truncate memory size if you tried to use 32MB of memory:
this would happen if system BIOS was shadowed and the hole disappeared if
shadowing was disabled in BIOS Setup. I doubt that it'll help here but....
I have just found a message in a mailing list archive:

http://www.clustermatic.org/pipermail/linuxbios/2004-January/006372.html

I have an Opteron machine based on the Tyan K8W S2885
mainboard which is equipped with 8GB of RAM (8x1GB DIMM).
The BIOS is mapping the PCI/AGP devices into the address
space immediately below 4GB and so consequently, I am losing
access to nearly an entire 1GB of RAM. I've spoken to Tyan
about this and they acknowledged that it it is principle
possible for the BIOS to remap the DIMM presently located
at 3GB to 9GB but that they have no intention of including
this option in their BIOS as it "penalizes 32-bit OS's that
cannot use more than 4GB."

Bogus excuse, BTW. If the BIOS had an option to chose either 32-bit
or 64-bit OS, each user could chose the configuration that suits
him best. BTW, I don't remember if the 32 bit mode of the AMD 64
is compatible with the 36-bit segmented mode of the Xeon (not sure
if the Pentiums also have that) ?

I read something similar at:
http://www.spinics.net/lists/amd64/msg00321.html

This seems to mean that there is not much hope, but OTOH, this
message is some months old. Maybe things have changed ?
Click to expand...

As you say, I think what needs to happen here is that the BIOS needs to be
changed to allow it to be set for 32-bit or 64-bit mode and to remap its
"reserved" high addressing to the 40bit mark as necessary. Another thing
here is whether the current PCI devices might lack the ability to be mapped
higher than 32-bit addressing. The mechanisms are in PCI specs but I've no
idea whether commonly implemened in current PCI cards.

Even if the hole is stuck at 4GB, I can't see why the BIOS would have to
just throw the 512MB of main memory away. Since all OSs use paging, surely
it would be possible to still use that 512MB by having the BIOS map it
above the hole - a 32-bit OS might not be able to use it then but a 64-bit
one would.

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??
 
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