Upgrading from 32 bit to 64 bit

[Rick Stevens]

On Thu, 2006-09-07 at 15:44 -0700, Waldher, Travis R wrote:
> > -----Original Message-----
> > From: Rick Stevens [mailto:rstevens at vitalstream.com] 
> > Sent: Thursday, September 07, 2006 1:47 PM
> > To: Getting started with Red Hat Linux
> > Subject: Re: Upgrading from 32 bit to 64 bit
> >
> > > On Thu, 2006-09-07 at 10:32 -0700, Waldher, Travis R wrote:
> > > What is involved for Redhat AS 4.0?
> > > 
> > > The system was initially built 32bit, but some users would like it
> > > running in 64.
> > > 
> > > Is it as simple as loading a different kernel? :fingerscrossed:
> >
> > Well, yeah, but most of your applications won't be accelerated that
> > much.  A full 64-bit system will have most of the utilities (/bin,
> > /sbin, /usr/bin, /usr/sbin, etc.) built with 64-bit as well as having
> > full 64-bit libraries (/usr/lib64 as well as /usr/lib).
> 
> Ok, so the only safe and reliable way for compilation work to get a
> performance gain will be to do a rebuild of the system.  Correct?

Well, yes.  Or install the 64-bit OS.  As I mentioned, 32-bit stuff will
run fine (provided you have the appropriate 32-bit libraries installed
as well), but the 64-bit specific stuff will go like greased lightning
out of hell.  Example: Full kernel compile on a 2GHz Opteron (Opteron
3000) takes about 10-12 minutes.  Same thing on a 2.8GHz Xeon takes well
over 25 minutes.

> If so, I was afraid of that...

Yup.  You didn't think there was a free lunch involved now, did you? :-)

Now, note that the 64-bit kernel WILL allow you to run more 32-bit apps
faster as it can access more memory directly and its memory management
(elevator code) is more efficient when context switching than the 32-bit
kernel.  It's not a significant difference, but its there.

IMHO, if you're going to go 64-bit, go 64-bit all the way.  Revert to
32-bit when you must.  Most Linux apps are available in 64-bit versions.
Some stuff isn't, but that's where the Athlon64/Opteron ability to run
both types simulaneously absolutely shines.  As I said, I use several
32-bit apps just fine (including Skype).  Really, once you go 64-bit,
it's REALLY hard to go back.  And if you can go 64-bit dual core,
well...  :-D

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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-  Time: Nature's way of keeping everything from happening at once.  -
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