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

[John Hodrien]

On Thu, 23 Jun 2005, Dave Fisher wrote:

> 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?

Well, how does an ice cream perform against a walnut whip?  Not a discussion
to bother with in depth here, there are too many variables.

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

There's no need to run in a chroot environment although you're free to if you
want.  Fedora sets things up somewhat similarly to IRIX, with /lib for 32bit
libraries and /lib64 for 64bit libraries, and you can freely use executables
without worrying what they are compiled for.

>> 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?

More than 4Gigs of RAM, tending towards 16.

> 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.

I'd stick with 32bit and save yourself some headaches, since you're not going
to be that worried about eeking the last gram out of machine anyhows.

jh

-- 
"I do not pretend to know where many ignorant men are sure - that is all that
  agnosticism means."                                 -- Clarence Darrow