gerben-s / quicksort-blog-post

Branchfree QuickSort performance analysis

This is not an officially supported Google product

This directory contains code and benchmarks accompanying the blog post about QuickSort performance.

The main() function validates the correctness of the main algorithms before running benchmarks.

The benchmark requires Bazel to build. At build time Bazel will automatically download and build the benchmarking framework.

From this directory, run:

$ CC=clang bazel build -c opt :bench_sort
$ ../bazel-bin/quicksort-blog-post/bench_sort

The versions of gcc I've run did not lower conditionals into branchfree code.

Overview of benchmarks

Random int's

Benchmark                                          Time           CPU Iterations
---------------------------------------------------------------------------------
BM_Sort<std::sort>                                79 ns         78 ns    9300000
BM_Sort<std::stable_sort>                         90 ns         90 ns    7400000
BM_Sort<std_heap_sort>                           130 ns        130 ns    4600000
BM_Sort<andrei::sort>                             52 ns         52 ns   15100000
BM_Sort<exp_gerbens::QuickSort>                   30 ns         30 ns   24700000
BM_Sort<pdqsort>                                  42 ns         42 ns   16800000
BM_Sort<HeapSort>                                 51 ns         51 ns   14500000

Random pointers sort on address (0 levels of indirection)

Benchmark                                              Time           CPU Iterations
---------------------------------------------------------------------------------
BM_IndirectionSort<0, std::sort>                      77 ns         77 ns    9200000
BM_IndirectionSort<0, std::stable_sort>               92 ns         91 ns    7600000
BM_IndirectionSort<0, std_heap_sort>                 124 ns        124 ns    5800000
BM_IndirectionSort<0, andrei::sort>                   56 ns         56 ns   10000000
BM_IndirectionSort<0, exp_gerbens::QuickSort>         32 ns         32 ns   18300000
BM_IndirectionSort<0, pdqsort_branchless>             40 ns         40 ns   17600000
BM_IndirectionSort<0, HeapSort>                       60 ns         60 ns   11900000

Random pointers sort on value pointed to (1 levels of indirection)

Benchmark                                              Time           CPU Iterations
-------------------------------------------------------------------------------------
BM_IndirectionSort<1, std::sort>                      97 ns         97 ns    7400000
BM_IndirectionSort<1, std::stable_sort>              133 ns        133 ns    5100000
BM_IndirectionSort<1, std_heap_sort>                 180 ns        180 ns    4100000
BM_IndirectionSort<1, andrei::sort>                   67 ns         67 ns   11600000
BM_IndirectionSort<1, exp_gerbens::QuickSort>         42 ns         42 ns   16300000
BM_IndirectionSort<1, pdqsort_branchless>             54 ns         54 ns   10000000
BM_IndirectionSort<1, HeapSort>                      131 ns        131 ns    6000000