[OpenMP] Limit number of dispatch buffers

[jlpeyton]

Summary

This patch limits the number of dispatch buffers (used for loop worksharing construct) to between 1 and 4096.

[hbae]

LGTM

openmp/runtime/src/kmp.h

 #define KMP_MIN_INTERVAL 0
 #define KMP_MAX_INTERVAL (INT_MAX - 1)
 #define KMP_DEFAULT_INTERVAL 0
 
 #define KMP_MIN_CHUNK 1
 #define KMP_MAX_CHUNK (INT_MAX - 1)
 #define KMP_DEFAULT_CHUNK 1
 
+#define KMP_MIN_DISP_NUM_BUFF 1
 #define KMP_DFLT_DISP_NUM_BUFF 7
+#define KMP_MAX_DISP_NUM_BUFF 4096
+
 #define KMP_MAX_ORDERED 8
 
 #define KMP_MAX_FIELDS 32
 
 #define KMP_MAX_BRANCH_BITS 31
 
 #define KMP_MAX_ACTIVE_LEVELS_LIMIT INT_MAX
 

openmp/runtime/src/kmp_csupport.cpp

 void kmpc_set_defaults(char const *str) {
   // __kmp_aux_set_defaults initializes the library if needed
   __kmp_aux_set_defaults(str, KMP_STRLEN(str));
 }
 
 void kmpc_set_disp_num_buffers(int arg) {
   // ignore after initialization because some teams have already
   // allocated dispatch buffers
-  if (__kmp_init_serial == 0 && arg > 0)
+  if (__kmp_init_serial == FALSE && arg >= KMP_MIN_DISP_NUM_BUFF &&
+      arg <= KMP_MAX_DISP_NUM_BUFF) {
     __kmp_dispatch_num_buffers = arg;
   }
+}
 
 int kmpc_set_affinity_mask_proc(int proc, void **mask) {
 #if defined(KMP_STUB) || !KMP_AFFINITY_SUPPORTED
   return -1;
 #else
   if (!TCR_4(__kmp_init_middle)) {
     __kmp_middle_initialize();
   }

openmp/runtime/src/kmp_ftn_entry.h

 }
 
 void FTN_STDCALL FTN_SET_DISP_NUM_BUFFERS(int KMP_DEREF arg) {
 #ifdef KMP_STUB
   ; // empty routine
 #else
   // ignore after initialization because some teams have already
   // allocated dispatch buffers
-  if (__kmp_init_serial == 0 && (KMP_DEREF arg) > 0)
-    __kmp_dispatch_num_buffers = KMP_DEREF arg;
+  int num_buffers = KMP_DEREF arg;
+  if (__kmp_init_serial == FALSE && num_buffers >= KMP_MIN_DISP_NUM_BUFF &&
+      num_buffers <= KMP_MAX_DISP_NUM_BUFF) {
+    __kmp_dispatch_num_buffers = num_buffers;
+  }
 #endif
 }
 
 int FTN_STDCALL FTN_SET_AFFINITY(void **mask) {
 #if defined(KMP_STUB) || !KMP_AFFINITY_SUPPORTED
   return -1;
 #else
   if (!TCR_4(__kmp_init_middle)) {

openmp/runtime/src/kmp_settings.cpp

 // -----------------------------------------------------------------------------
 // KMP_DISP_NUM_BUFFERS
 static void __kmp_stg_parse_disp_buffers(char const *name, char const *value,
                                          void *data) {
   if (TCR_4(__kmp_init_serial)) {
     KMP_WARNING(EnvSerialWarn, name);
     return;
   } // read value before serial initialization only
-  __kmp_stg_parse_int(name, value, 1, KMP_MAX_NTH, &__kmp_dispatch_num_buffers);
+  __kmp_stg_parse_int(name, value, KMP_MIN_DISP_NUM_BUFF, KMP_MAX_DISP_NUM_BUFF,
+                      &__kmp_dispatch_num_buffers);
 } // __kmp_stg_parse_disp_buffers
 
 static void __kmp_stg_print_disp_buffers(kmp_str_buf_t *buffer,
                                          char const *name, void *data) {
   __kmp_stg_print_int(buffer, name, __kmp_dispatch_num_buffers);
 } // __kmp_stg_print_disp_buffers
 
 #if KMP_NESTED_HOT_TEAMS

openmp/runtime/test/env/kmp_dispatch_buf_range.c

+// RUN: %libomp-compile
+// RUN: env KMP_DISP_NUM_BUFFERS=0 %libomp-run 2>&1 | FileCheck --check-prefix=SMALL %s
+// RUN: env KMP_DISP_NUM_BUFFERS=4097 %libomp-run 2>&1 | FileCheck --check-prefix=LARGE %s
+// SMALL: OMP: Warning
+// SMALL-SAME: KMP_DISP_NUM_BUFFERS
+// SMALL-SAME: too small
+// LARGE: OMP: Warning
+// LARGE-SAME: KMP_DISP_NUM_BUFFERS
+// LARGE-SAME: too large
+#include <stdio.h>
+#include <stdlib.h>
+
+int main() {
+  int i;
+  #pragma omp parallel for
+  for (i = 0; i < 1000; i++) {}
+  return EXIT_SUCCESS;
+}