Advanced Micro Devices Inc (AMD)

[HailMary]

Well I just ran some simple tests on Linux for grins.

I compiled up an off-the-shelf standalone qsort c program using gcc and various targets. I sorted 100M randomly generated integers, and I used the same set of integers for each run.

The systems are identical other than one is using x86-64 Linux. The base versions are the same. Running Opteron 246's with 4G of memory. This benchmark is not memory constrained in any way.

I took the average of 3 runs for each. The deviation was around 1/4 second for each run. Note that a significant portion of the time below is just reading in the file that contains the 100M random integers. I intend to benchmark again with this factored out, as it will probably multiply the percentages below by a factor of 2.

                 
 o/s     app     optimized  runtime      performance 
                 compile?                increase 
 ---------------------------------------------------- 
 32-bit  32-bit  no         97  seconds  baseline 
 64-bit  32-bit  no         94  seconds  +3% 
 64-bit  64-bit  no         110 seconds  -13% 
  
 32-bit  32-bit  yes        84  seconds  baseline 
 64-bit  32-bit  yes        81  seconds  +4% 
 64-bit  64-bit  yes        70  seconds  +17% 
 

The optimized app utilizes the extra registers available in 64-bit mode. The unoptimized 64-bit app takes a hit due to larger pointers, etc., as expected. Note how the 32-bit app without a recompile actually runs slightly faster on the 64-bit os. I expect the same from Windows. Actually I expect more of an improvement because I think Windows system code can be optimized more than Linux can.

The data above shows that 64-bit vs. 32-bit hurts this app, but the extra registers in x86_64 more than make up for it. Apps that need 64-bit data structures will likely have a gain instead of a loss. Maybe for my next test I'll qsort 64 bit integers.