diff options
Diffstat (limited to 'src/sort.c')
| -rw-r--r-- | src/sort.c | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/src/sort.c b/src/sort.c index 13954cbbc..9b8666afb 100644 --- a/src/sort.c +++ b/src/sort.c @@ -109,12 +109,16 @@ struct rlimit { size_t rlim_cur; }; and is responsible for merging TOTAL lines. */ #define MAX_MERGE(total, level) (((total) >> (2 * ((level) + 1))) + 1) -/* Heuristic value for the number of lines for which it is worth - creating a subthread, during an internal merge sort, on a machine - that has processors galore. Currently this number is just a guess. - This value must be at least 4. We don't know of any machine where - this number has any practical effect. */ -enum { SUBTHREAD_LINES_HEURISTIC = 4 }; +/* Heuristic value for the number of lines for which it is worth creating + a subthread, during an internal merge sort. I.e., it is a small number + of "average" lines for which sorting via two threads is faster than + sorting via one on an "average" system. On an dual-core 2.0 GHz i686 + system with 3GB of RAM and 2MB of L2 cache, a file containing 128K + lines of gensort -a output is sorted slightly faster with --parallel=2 + than with --parallel=1. By contrast, using --parallel=1 is about 10% + faster than using --parallel=2 with a 64K-line input. */ +enum { SUBTHREAD_LINES_HEURISTIC = 128 * 1024 }; +verify (4 <= SUBTHREAD_LINES_HEURISTIC); /* The number of threads after which there are diminishing performance gains. */ |