Re: AMD64-generic doesn't see all 4GB RAM?

[Andrew Sharp <andy@netfall.com>]

On Mon, Nov 06, 2006 at 08:26:35PM +0100, Goswin von Brederlow wrote:

> > There is almost never a reason to not run one of debian's prebuilt
> > kernels.  They work perfectly and optimally for probably 99% of users.
> 
> I only know of two (in my eyes) valid reasons to build your own kernel:
> 
> 1. you hate initrd since it too often doesn't work
> 2. you need/want some extra patch

There is at least a couple of other reasons ~:^)

One is the Debian removes some things they find objectionable from
the stock kernel sources.  A really good example is USB serial dongle
support.  The Debian kernels have almost all of them removed, probably
because they object to the firmware license agreement, or lack thereof.
But they are in the stock kernel and so if you need to use one of them
you have to build your own kernel, not from Debian kernel sources.

Lately, I cannot get USB storage or hubs to work on the stock kernel,
unless I do an install and select 'desktop environment' in tasksel. Yuck.

> The "stock" kernels aren't slower and the disk space wasted for
> unneeded (for you) modules is irelevant on any modern harddisk. The
> times when you rebuild your kernel to get a slimmer one and save
> memory are long gone. And on amd64 there is no change in optimizations

Except maybe on embedded systems.  Yes, there are opteron based embedded
systems.  OK, not a good example, sorry.

This thread originated with a problem getting all the physical mem on a
Tyan S2877.  Now I have one of these, and I experienced the same
problem.  The problem is that the Bios doesn't say "enable IOMMU", it
says "map memory hole?" and your options are
'DISABLED|software|hardware' and no explanation.  Lame Bios help text,
as always.  And it shouldn't be disabled by default either.  Sheez.

My question is, what is the difference between the 'hardware' and
'software' choices?  Is there a performance implication?  Please don't
reply with speculations, I can speculate myself just fine ~:^)

Cheers,

a