[EMAIL PROTECTED] wrote:
Read the sources and the cpu specs. Benchmarking such problems is virtually impossible.If the memset bypasses the cache then the following access will cause a cache line miss, which can be so slow that using the faster memset can result in a net performance loss.
Could you suggest some structs to test? If I get your meaning, I would make a loop that sets then reads from the structure.
I don't have OS-X, thus I checked the Linux-kernel sources: It seems that the power architecture doesn't have the same problem as x86.
There is a special clear cacheline instruction for large memsets and the rest is done through carefully optimized store byte/halfword/word/double word sequences.
Thus I'd check what happens if you memset not perfectly aligned buffers. That's another point where over-optimized functions sometimes break down. If there is no slowdown, then I'd replace the postgres function with the OS provided function.
I'd add some __builtin_constant_p() optimizations, but I guess Tom won't like gcc hacks ;-)
--
Manfred
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