[FFmpeg-devel] [PATCH] avfilter/vf_deshake: replace qsort with AV_QSORT

[Ganesh Ajjanagadde]

qsort is called indirectly in filter_frame, suggesting its performance
criticality. AV_QSORT is substantially faster due to the inlining of the
comparison callback. Thus, the increase in performance should be worth
the increase in binary size.

Sample benchmark (x86-64, Haswell, GNU/Linux):
File: original from https://trac.ffmpeg.org/ticket/1430
command: ffmpeg -stream_loop 8 -i file.webm -vf deshake=rx=64:ry=64 -f null -

Timer truncated at 1024 runs.
new:
28260 decicycles in qsort,       1 runs,      0 skips
35570 decicycles in qsort,       2 runs,      0 skips
39010 decicycles in qsort,       4 runs,      0 skips
46897 decicycles in qsort,       8 runs,      0 skips
40442 decicycles in qsort,      16 runs,      0 skips
41611 decicycles in qsort,      32 runs,      0 skips
40345 decicycles in qsort,      64 runs,      0 skips
38967 decicycles in qsort,     128 runs,      0 skips
38647 decicycles in qsort,     256 runs,      0 skips
40238 decicycles in qsort,     512 runs,      0 skips
39676 decicycles in qsort,    1024 runs,      0 skips

old:
1740280 decicycles in qsort,       1 runs,      0 skips
 923560 decicycles in qsort,       2 runs,      0 skips
 511330 decicycles in qsort,       4 runs,      0 skips
 309720 decicycles in qsort,       8 runs,      0 skips
 194900 decicycles in qsort,      16 runs,      0 skips
 142686 decicycles in qsort,      32 runs,      0 skips
 112516 decicycles in qsort,      64 runs,      0 skips
  98166 decicycles in qsort,     128 runs,      0 skips
  88147 decicycles in qsort,     256 runs,      0 skips
  88706 decicycles in qsort,     512 runs,      0 skips
  86783 decicycles in qsort,    1024 runs,      0 skips

Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
---
 libavfilter/vf_deshake.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libavfilter/vf_deshake.c b/libavfilter/vf_deshake.c
index 885569a..e32436d 100644
--- a/libavfilter/vf_deshake.c
+++ b/libavfilter/vf_deshake.c
@@ -57,6 +57,7 @@
 #include "libavutil/mem.h"
 #include "libavutil/opt.h"
 #include "libavutil/pixdesc.h"
+#include "libavutil/qsort.h"
 
 #include "deshake.h"
 #include "deshake_opencl.h"
@@ -106,7 +107,7 @@ static double clean_mean(double *values, int count)
     int cut = count / 5;
     int x;
 
-    qsort(values, count, sizeof(double), cmp);
+    AV_QSORT(values, count, double, cmp);
 
     for (x = cut; x < count - cut; x++) {
         mean += values[x];
-- 
2.6.2