Performance of 64-bit vs. 32-bit Windows Dual Core

mikemuch writes "ExtremeTech's Loyd Case has done extensive testing on the same dual-core Athlon X2 4800+ system to explore performance differences between Windows XP Professional x64 and good ole Win32. The biggest hurdle is getting the right drivers. There are a few performance surprises, particularly in 3D games."

Comments

Plenty of time to wait for 64 bit apps.

[Godeke]

The good this article tells us is that the 64 bit OS doesn't cause any significant loss of performance for the 32 bit applications that will function under it. On the other hand, the only 64 bit to 32 bit comparisons they have also show almost no differences. I think this is the most telling:

The good news is that 32-bit Far Cry (as of the 1.31 patch) runs fine under Windows 64-bit mode, with very little performance penalty. When we move to the base 64-bit version, we pick up a couple of frames per second at 1280x1024, but we defy anyone to actually notice the difference between 79.5 and 82 fps.

The good news is that the enhanced version still clocks in at 80 fps. This bodes well for 64-bit gaming, as game developers can add substantial new content and detail without sacrificing performance.

Desktop applications (even games) don't need the one thing that 64 bit computing really excels at: massive addressing space. A database server that is compiled to 64 bit code will have access to much more RAM, and thus have much better performance if RAM bound (which many DBs are). Meanwhile for POV-Ray the fastest result of 383 seconds was the 32bit application on 64 OS!

I think that it is safe to hold off on 64 bit for your personal desktop until a larger share of applications are compiled with 64 bit optimizations, but unlike the 16 -> 32 bit shift, I suspect the results will be underwhelming except for extremely memory consuming applications.

After reading the benchmarks...

[vandy1]

I can only conclude that they made no attempt to use the extra registers. Of *course* an f'ing 32-bit system will outpace a 64-bit system; Why do you think most Solaris apps are still 32-bit?

The reason why x86-64 is a win is because there are more registers as well. This allows compilers to do a better job.

Standard phallacy

[vlad_petric]

The main performance gain from going to x86-64 does not come from larger operands and larger addressing space. It comes from a cleaned-up instruction set architecture and, most importantly, from a larger set of registers. x86-64 has 16 general-purpose registers whereas x86-32 arguably has about 7 GPRs. For x86-32, a compiler generally allocates 2 or at most 3 registers to variables. For x86-64, it can utilize ~12. This greatly reduces the number of loads and stores to the stack. The performance gain comes from the fact that it's much faster to communicate via a register than through memory.

BTW, I don't know about windoze, but in the Linux world going from 32 bits to 64 bits almost always seems to produce a performance gain of 10->20%. I personally tried a simulator I'm using with 64 bits (recompiled with gcc), and got a speedup of 12%.

Coding practices need rethinking...

[mi]

Complex data-structures involve a lot of pointers -- all of which are twice bigger on 64-bit machines. Sometimes, this makes the pointers bigger (or comparable) to the structures themselves.

Most obvious are char * fields. If the string is 8 characters or less, it is cheaper to just store in the structure (and pass by value, where possible).

Considering, that most such strings (and substructures) are malloc-ed (with a couple of pointers worth of malloc's overhead), the case for embedding them becomes even stronger...