[Wylug-discuss] Linux on Intel 64-Bit Xeon

[Dave Fisher]

On Thu, Jun 23, 2005 at 01:49:49PM +0100, John Hodrien wrote:
> On Thu, 23 Jun 2005, Neil Pilgrim wrote:
> >So are you saying that the EM64T intel chips don't allow running in 32- 
> >and 64-bits 'simultaneously'? I'm intrigued because I run some 32-bit apps 
> >here on my athlon64 running debian, in an i386 chroot (with i386 debs), at 
> >the 'same' time as the rest of the system is running in 64-bit mode, ie. 
> >with the 64-bit debs. Are you saying that while the EM64T is a compatible 
> >arch to amd 64-bit, it can't do this?
> 
> I think this is a misunderstanding of how it all works.  Benchmarks on our
> EM64T box show that 32bit code can run a squidgeon (new SI unit) faster in
> 64bit mode than 32bit.  Nothing that I'd bother about, but certainly not
> slower.


How does the EM64T perform compared with AMD64 in 64-bit mode?  

... and what is the yes/no answer to Neil's question about the
feasability of running 32-bit binaries in a chroot environment?

I could probably live with 64-bit debs plus Xen virtualisation, if
necessary.

> >I thought the only software emulation required was if you run 32-bit
> >on Itanium?
> 
> Indeed.
> 
> >If I follow what you're saying, then I'm glad I didn't buy an EM64T
> >chip!
> 
> I wouldn't be glad at all.  You don't lose in any way by having the
> extensions, as you're always free to not use them.  The performance of
> a large memory machine does however suck (as I understand things) on
> EM64T compared to AMD64.

What consitutes 'large memory' in this case?  

I am primarily concerned with web server performance for what will
initially be fairly low traffic database-driven sites.  Few of the sites
are ever likely to get more than a few tens of thousands of page
impressions per day.

I was thinking of something like 2G of memory.

Dave