amd64 slower than i386 on identical AMD 64 system?

JoaoBR joao at
Tue Mar 14 12:27:22 UTC 2006

On Tuesday 14 March 2006 08:49, ray at wrote:
> At 12:38 PM 3/14/2006 +0100, Alexander Konovalenko wrote:
> | On Tuesday 14 March 2006 11:40, JoaoBR wrote:
> | > so where is your comparism? My point was that the same hardware is
> | > faster running i386
> | >
> | I have experienced that -O3 and -ffast-math optimizations flags on AMD64
> | might cause degrade in performance, meaning that -O2 is the fastest. When
> | you compile your ports what opt. flags do you use? Try to reinstall
> | ubench with different flags. Also code produced with gcc4.x is faster
> | then system compiler and has no degrade effect. Some time ago I was
> | interested in fast scientific computations and did some primitive
> | benchmark tests
> | (
> |
> | I just wonder what will happen if you run ubench (compiled for i386) on
> | AMD64, will performance overcome amd64 ubench?
> |

and what would be the point here? 

the amd64 systems I checked are running amd64
the i386 systems I checked are running i386

and entirely I mean

> I'm just coming in on the tail end of the message (missed the previous
> stuff). I recently did some benchmarks between AMD64 and i386 (version 5.4)
> on the same hardware.  I initially saw that the i386 ran faster also. 
> However, after searching a bit further, I discovered that I had made an
> error: the i386 kernel has the SMP stuff compiled into the generic kernel
> by default, while the AMD64 (at least on 5.4) does not.  It has a separate
> kernel file called SMP (as I recall), which adds the SMP line and then does
> an include for the rest of the generic kernel config file (or something to
> that effect).
> Anyway, if you are testing back and forth, it's easy to forget that and end
> up accidently testing an i386 with SMP against an AMD64 without SMP.

obviously I checked UP kernels against UP and SMP against SMP
but anyway running SMP kernel on single processor systems should not affect 
this tests


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