Sculpt/dyntopo: Make the omp threads configurable to overcome performance issues

- autodetect optimal default, which typically avoids HT threads
- can store setting in .blend per scene
- this does not touch general omp max threads, due i found other areas where the calculations are fitting for huge corecount
- Intel notes, some of the older generation processors with HyperThreading would not provide significant performance boost for FPU intensive applications. On those systems you might want to set OMP_NUM_THREADS = total number of cores (not total number of hardware theads).

1 files changed, 32 insertions, 1 deletions

diff --git a/source/blender/blenlib/intern/threads.c b/source/blender/blenlib/intern/threads.c
index ded2fd7e06d..78752fde608 100644
--- a/source/blender/blenlib/intern/threads.c
+++ b/source/blender/blenlib/intern/threads.c
@@ -54,10 +54,25 @@
 #  include <sys/time.h>
 #endif
 
-#if defined(__APPLE__) && defined(_OPENMP) && (__GNUC__ == 4) && (__GNUC_MINOR__ == 2) && !defined(__clang__)
+#ifdef _OPENMP
+#include <omp.h>
+#endif
+
+#if defined(__APPLE__)
+#if defined(_OPENMP) && (__GNUC__ == 4) && (__GNUC_MINOR__ == 2) && !defined(__clang__)
 #  define USE_APPLE_OMP_FIX
 #endif
 
+/* how many cores not counting HT aka pysical cores */
+static int system_physical_thread_count(void)
+{
+	int ptcount;
+	size_t ptcount_len = sizeof(ptcount);
+	sysctlbyname("hw.physicalcpu", &ptcount, &ptcount_len, NULL, 0);
+	return ptcount;
+}
+#endif // __APPLE__
+
 #ifdef USE_APPLE_OMP_FIX
 /* ************** libgomp (Apple gcc 4.2.1) TLS bug workaround *************** */
 extern pthread_key_t gomp_tls_key;
@@ -335,6 +350,22 @@ void BLI_end_threads(ListBase *threadbase)
 
 /* System Information */
 
+/* gets the number of openmp threads the system can make use of */
+int BLI_omp_thread_count(void)
+{
+	int t;
+#ifdef _OPENMP
+#ifdef __APPLE__
+	t = system_physical_thread_count();
+#else
+	t = omp_get_num_procs();
+#endif
+#else
+	t = 1;
+#endif
+	return t;
+}
+
 /* how many threads are native on this system? */
 int BLI_system_thread_count(void)
 {