Re:Should programmers learn machine code?
by amalcon on Sunday September 06, 2009 @01:13AM
(#807489)
Really, not many people even think about what's in any level lower than the one they're working on.
Case in point: I once had a C++ program in which replacing malloc() with a wrapper that rounded up all allocations over 1kb to multiples of 1kb actually increased execution speed by 20%. Those may not have been the exact numbers, but that's the general idea. Guess why.
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The program was allocating many large objects with small variations in size. The system default malloc/free implementation would work efficiently for small objects, but would store large allocations in a linked list, bucketed by size. In the worst-case (all objects are large and of different sizes), freeing n objects would take O(n^2) time. This program came very close to that ideal. The rounding prevented that worst case by using fewer buckets.
Of course, that version never saw production use. It was just used to demonstrate the nature of this particular performance problem.
Case in point: I once had a C++ program in which replacing malloc() with a wrapper that rounded up all allocations over 1kb to multiples of 1kb actually increased execution speed by 20%. Those may not have been the exact numbers, but that's the general idea. Guess why.
. . .
The program was allocating many large objects with small variations in size. The system default malloc/free implementation would work efficiently for small objects, but would store large allocations in a linked list, bucketed by size. In the worst-case (all objects are large and of different sizes), freeing n objects would take O(n^2) time. This program came very close to that ideal. The rounding prevented that worst case by using fewer buckets.
Of course, that version never saw production use. It was just used to demonstrate the nature of this particular performance problem.