sort: parallelize internal sort

This patch is by Gene Auyeung, Chris Dickens, Chen Guo, and Mike
Nichols, based off of a patch by Paul Eggert, Glen Lenker, et. al.,
with a basic heap implementation based off of the GDSL heap,
originally by Nicolas Darnis.

The number of sorts done in parallel is limited to the number
of available processors by default, or can be further restricted
with the --parallel option.

On a dual-die, 8 core Intel Xeon, results show sorting with
8 threads is almost 4 times faster than using a single thread.
Timings when sorting a 96MB file:
THREADS     TIME (s)
1            5.10
2            2.87
4            1.75
8            1.31

Single threaded sorting has also been improved,
especially for cheaper comparison operations:
COMMAND             BEFORE (s)  AFTER (s)
sort                 8.822       8.716
sort -g             10.336      10.222
sort -n              3.077       2.961
LANG=C sort          2.169       2.066

* bootstrap.conf: Add heap, pthread.
* coreutils.texi (sort): Describe the new --parallel option.
* gl/lib/heap.c: New file. Very basic heap implementation.
* gl/lib/heap.h: New file.
* gl/modules/heap: New file.
* src/Makefile.am: Add LIB_PTHREAD.
* src/sort.c: Include heap.h, nproc.h, pthread.h.
(MAX_MERGE): New macro.
(SUBTHREAD_LINES_HEURISTIC, PARALLEL_OPTION): New constants.
(MERGE_END, MERGE_ROOT): New constants.
(struct merge_node): New struct.
(struct merge_node_queue): New struct.
(sortlines temp): Remove declaration.
(usage, long_options, main): New option, --parallel.
(specify_nthreads): New function.
(mergelines): New signature, to emphasize the fact that the HI area
must be part of the destination.  All callers changed.
(sequential_sort): New function, renamed from sortlines. Merge in
the functionality of sortlines_temp.
(compare_nodes): New function.
(lock_node, unlock_node): New functions.
(queue_destroy): New function.
(queue_init): New function.
(queue_insert): New function.
(queue_pop): New function.
(write_unique): New function.
(mergelines_node): New function.
(check_insert): New function.
(update_parent): New function.
(merge_loop): New function.
(sortlines): Rewrite to support and use parallelism, with a new
signature. All callers changed.
(struct thread_args): New struct.
(sortlines_thread): New function.
(sortlines_temp): Remove.
(sort): New argument NTHREADS. All uses changed. Output moved to
mergelines_node.
(main): disable threading if we are sorting at random.
* tests/Makefile.am (TESTS): Add misc/sort-benchmark-random.
* tests/misc/sort-benchmark-random: New file.

Signed-off-by: Pádraig Brady <P@draigBrady.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 21cf36d1d..942978f33 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -4068,6 +4068,14 @@ have a large sort or merge that is I/O-bound, you can often improve
 performance by using this option to specify directories on different
 disks and controllers.
 
+@item --parallel=@var{n}
+@opindex --parallel
+@cindex multithreaded sort
+Limit the number of sorts run in parallel to @var{n}. By default,
+@var{n} is set to the number of available processors, and values
+greater than that are reduced to that limit. Also see
+@ref{nproc invocation}.
+
 @item -u
 @itemx --unique
 @opindex -u
@@ -4163,6 +4171,13 @@ sort -n -r
 @end example
 
 @item
+Run no more that 4 sorts concurrently, using a buffer size of 10M.
+
+@example
+sort --parallel=4 -S 10M
+@end example
+
+@item
 Sort alphabetically, omitting the first and second fields
 and the blanks at the start of the third field.
 This uses a single key composed of the characters beginning