Benchmarks: AMD64 vs i386 on Dual 246 Opteron

[ray at redshift.com]

At 09:01 AM 7/28/2005 -0600, Ken Gunderson wrote:
| On Thu, 28 Jul 2005 14:13:49 +0200
| des at des.no (Dag-Erling Smørgrav) wrote:
| 
| > ray at redshift.com writes:
| > > While this sounded like a long shot, I loaded FreeBSD 5.4 i386 on
| > > the machine and after applying the exact same configuration to the
| > > OS, Apache, PHP and MySQL, re-ran the benchmarks.  Much to my
| > > surprise, just changing the OS from 64 bit to 32 bit caused the
| > > machine to double in speed.  The results are attached in an Excel
| > > spreadsheet.  So the exact same machine, running the identical
| > > configuration, performed roughly twice as fast when running FreeBSD
| > > 5.4 i386 vs FreeBSD 5.4 AMD64.  Something about this seems so wrong
| > > to me :-)
| > 
| > 64-bit code uses up to twice as much CPU cache and twice as many
| > memory accesses to do the same work as the equivalent 32-bit code.
| 
| Makes a lot of sense once you think about it but counter intuitive to
| most people's expectations from their "shinny new 64bit powerhouse"...
| 
| Looking at the other side of the coin perhaps we should mention some
| situations where 64bit os's outperform 32 bit ones, e.g.
| analysis of larger, complex datasets...??
| 
| I've talked with a few folks from the SAP crowd and they're absolutely
| in love with the Opterons, reporting far superior performance over
| Xeons, and are rolling out quads and 8x in lieu of much, much, much more
| costly heavy iron counter parts.  They are, however, running on Linux.
| 
| Ubench scores, for what they're worth, appear to be comparable between
| Opterons and Xeon64T's , so I guess the answer depends on your
| application.;-)

I've also heard the AMD's perform well under heavy database load - although I
have not put any machine into production yet.  

As you say, you get a new shinney AMD and run to put a 64 bit OS on it thinking
it will smoke the tires.  But once you test it and start thinking about it, the
32 bit running faster makes sense.  Maybe there needs to be a 20 bit OS :-)

Anyway, thanks for the run down.

Ray