AMD64 I386 or X64 load?

[Ewan Mac Mahon]

On Sun, Mar 26, 2006 at 07:10:25PM -0500, stan wrote:
> On Mon, Mar 27, 2006 at 10:35:11AM +1100, James Gray wrote:
> > On Mon, 27 Mar 2006 10:18 am, stan wrote:
> > > I just discovered that I grabbed the wrong set of CD's yesterday and loaded
> > > the I386 set on my dual processor, dual core Opteron machine (Sun Ultra
> > > 40).
> > >
> > > I then downloaded the latest 2.16 kernel and built a custom kernel for this
> > > machine, setting the processor type correctly in the kernel config.
> > >
Any particular reason for building your own?

> > > How much performance penalty should I expect, if I don't reload the correct
> > > binaries?
> > 
Depends entirely on the workload. Presumably you didn't buy a box like
that without some idea what you were going to run on it?

> > Pretty significant considering an AMD64 kernel wont grok 32bit libs.  IOW, it 
> > probably wont boot.  Install the 64bit kernel and libs and you'll be all set.
> > 
> 
It should boot fine; there's no reason you can't use a 64bit kernel and
a 32bit userspace. It's the normal mode of operation on most 64bit
architectures (amd64 being the exception) and if you couldn't do it on
amd64 the usual chroot trick for 32bit only apps wouldn't work.

> Mmm, something's not quite right here.
> 
> I _mistakenly_ loaded from the I386 CD's, and before I noticed it, I
> downloaded the 2.16 kernel sources, and built a kerne specifying the correct
> procesor. Hmm, maybe it's a 32 bit kernel now that I think about it.
>
It could be 64bit. The gcc included in 32bit x86 Ubuntu is capable of
generating 64bit code for amd64 - strange but true.
 
> How can I tell?
>
uname should tell you what architecture the kernel thinks it was built
for. Alternatively unless there's any particular reason why not, you
might consider installing a prebuilt kernel from the Ubuntu packages, so
you know exactly what you're getting.

Ewan

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