[Openmp-commits] [openmp] 7b8130c - [OpenMP][VE] Limit the number of threads to create (#66729)

[via Openmp-commits]

Author: Kazushi Marukawa
Date: 2023-09-20T17:44:24+09:00
New Revision: 7b8130c2c38b54e93af6c9aeacd954f2085abd33

URL: https://github.com/llvm/llvm-project/commit/7b8130c2c38b54e93af6c9aeacd954f2085abd33
DIFF: https://github.com/llvm/llvm-project/commit/7b8130c2c38b54e93af6c9aeacd954f2085abd33.diff

LOG: [OpenMP][VE] Limit the number of threads to create (#66729)

VE supports up to 64 threads per a VE process. So, we limit the number
of threads defined by KMP_MAX_NTH. We also modify the __kmp_sys_max_nth
initialization to use KMP_MAX_NTH as a limit.

Added: 
    

Modified: 
    openmp/runtime/src/kmp.h
    openmp/runtime/src/z_Linux_util.cpp

Removed: 
    


################################################################################
diff  --git a/openmp/runtime/src/kmp.h b/openmp/runtime/src/kmp.h
index b931b7ba66416ec..339e4ca4be6b350 100644
--- a/openmp/runtime/src/kmp.h
+++ b/openmp/runtime/src/kmp.h
@@ -1153,8 +1153,15 @@ extern void __kmp_init_target_task();
 #if defined(PTHREAD_THREADS_MAX) && PTHREAD_THREADS_MAX < INT_MAX
 #define KMP_MAX_NTH PTHREAD_THREADS_MAX
 #else
+#ifdef __ve__
+// VE's pthread supports only up to 64 threads per a VE process.
+// Please check p. 14 of following documentation for more details.
+// https://sxauroratsubasa.sakura.ne.jp/documents/veos/en/VEOS_high_level_design.pdf
+#define KMP_MAX_NTH 64
+#else
 #define KMP_MAX_NTH INT_MAX
 #endif
+#endif
 #endif /* KMP_MAX_NTH */
 
 #ifdef PTHREAD_STACK_MIN

diff  --git a/openmp/runtime/src/z_Linux_util.cpp b/openmp/runtime/src/z_Linux_util.cpp
index 42488eb6be5dc87..478c09baa1beefe 100644
--- a/openmp/runtime/src/z_Linux_util.cpp
+++ b/openmp/runtime/src/z_Linux_util.cpp
@@ -1894,6 +1894,13 @@ void __kmp_runtime_initialize(void) {
 
     /* Query the maximum number of threads */
     __kmp_type_convert(sysconf(_SC_THREAD_THREADS_MAX), &(__kmp_sys_max_nth));
+#ifdef __ve__
+    if (__kmp_sys_max_nth == -1) {
+      // VE's pthread supports only up to 64 threads per a VE process.
+      // So we use that KMP_MAX_NTH (predefined as 64) here.
+      __kmp_sys_max_nth = KMP_MAX_NTH;
+    }
+#else
     if (__kmp_sys_max_nth == -1) {
       /* Unlimited threads for NPTL */
       __kmp_sys_max_nth = INT_MAX;
@@ -1901,6 +1908,7 @@ void __kmp_runtime_initialize(void) {
       /* Can't tell, just use PTHREAD_THREADS_MAX */
       __kmp_sys_max_nth = KMP_MAX_NTH;
     }
+#endif
 
     /* Query the minimum stack size */
     __kmp_sys_min_stksize = sysconf(_SC_THREAD_STACK_MIN);