[Summary] Performance 32- vs. 64-bit kernel

-----Original POST -----

Is there a definitive advantage or disadvantage to running the 64-bit kernel
versus the 32-bit kernel on UltraSPARC I and II chips?

Noticeable performance difference, particularly running 32-bit applications
on
the 64-bit kernel?

I ran across an application's web site that reported a 30% reduction in speed
when running on the 64-bit kernel and was wondering if this was commonplace.

-------------------------------------

Thanks to my "quick poll" responders:
Rene OCCELLI
Kevin Buterbaugh
Darren Dunham
Lumpkin, Buddy

I doubted there would be a consensus, and there wasn't :-).

1) Probably the best answer, benchmark in the appropriate environment with the
appropriate applications. Your mileage may vary.
2) Majority reported that running a 32-bit application on the 64-bit kernel
requires more cycles to do alignment and byte packing operations. Thus it is
reasonable that 32-bit code would run slower on the 64-bit kernel than the
32-bit kernel.
3) Following #2's lead, the cache is half-sized in terms of number of words on
the 64-bit kernel since the word size is 64 bits instead of 32 bits. This can
cause more cache misses and degrade performance.
4) One reported floating point operations double in performance when the
application is compiled for 64-bit and (obviously) running on the 64-bit
kernel versus the app's 32/32 counterpart.
5) The 64-bit kernel allows the address space to grow beyond 4GB and this can
enhance performance by allowing more operations in the VM space rather than
forcing the operation to disk. Oracle hash join was given as an example.

Thanks, and have a nice day.
--Jim
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