[FFmpeg-devel] [PATCH] slicethread: Limit the automatic number of threads to 16

[Martin Storsjö]

This matches a similar cap on the number of automatic threads
in libavcodec/pthread_slice.c.

On systems with lots of cores, this does speed things up in
general (measurable on the level of the runtime of running
"make fate"), and fixes a couple fate failures in 32 bit mode on
such machines (where spawning a huge number of threads runs
out of address space).
---
 libavutil/slicethread.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libavutil/slicethread.c b/libavutil/slicethread.c
index ea1c9c8311..115b099736 100644
--- a/libavutil/slicethread.c
+++ b/libavutil/slicethread.c
@@ -24,6 +24,8 @@
 #include "thread.h"
 #include "avassert.h"
 
+#define MAX_AUTO_THREADS 16
+
 #if HAVE_PTHREADS || HAVE_W32THREADS || HAVE_OS2THREADS
 
 typedef struct WorkerContext {
@@ -105,7 +107,7 @@ int avpriv_slicethread_create(AVSliceThread **pctx, void *priv,
     if (!nb_threads) {
         int nb_cpus = av_cpu_count();
         if (nb_cpus > 1)
-            nb_threads = nb_cpus + 1;
+            nb_threads = FFMIN(nb_cpus + 1, MAX_AUTO_THREADS);
         else
             nb_threads = 1;
     }
-- 
2.25.1