3 ms·
The single-thread performance of the parallel prefix sum that they use is O(N log N), so the improvement from that to O(log N) on N threads is not as surprising
by TimorousBestie 1y ago
The single-thread performance of the parallel prefix sum that they use is O(N log N), so the improvement from that to O(log N) on N threads is not as surprising.
The way the headline is written, it sounds like Amdahl’s law was violated. It wasn’t, of course.
- casta 1y agoHow's the prefix sum on a single thread O(N log(N))? Isn't it trivially O(N)? It's just a for loop.
- TimorousBestie 1y agoYes, but for loop comes with all those data dependencies that prevent it from being parallelized trivially. The algorithm with fewer data dependencies is O(N log N). This is covered in more detail in the article.
- gyrovagueGeist 1y agoIt's from the depth of the computation, not the work