[Openmp-commits] [PATCH] D35490: Cleanup: two consecutive PAUSE instructions per spin loop iteration replaced with single one

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This revision was automatically updated to reflect the committed changes.
Closed by commit rL308423: OpenMP RTL cleanup: two PAUSEs per spin loop iteration replaced with single one (authored by achurbanov).

Changed prior to commit:
  https://reviews.llvm.org/D35490?vs=106887&id=107268#toc

Repository:
  rL LLVM

https://reviews.llvm.org/D35490

Files:
  openmp/trunk/runtime/src/kmp.h
  openmp/trunk/runtime/src/kmp_wait_release.h


Index: openmp/trunk/runtime/src/kmp.h
===================================================================
--- openmp/trunk/runtime/src/kmp.h
+++ openmp/trunk/runtime/src/kmp.h
@@ -1040,7 +1040,11 @@
 #if KMP_ARCH_X86
 extern void __kmp_x86_pause(void);
 #elif KMP_MIC
-static void __kmp_x86_pause(void) { _mm_delay_32(100); }
+// Performance testing on KNC (C0QS-7120 P/A/X/D, 61-core, 16 GB Memory) showed
+// regression after removal of extra PAUSE from KMP_YIELD_SPIN(). Changing
+// the delay from 100 to 300 showed even better performance than double PAUSE
+// on Spec OMP2001 and LCPC tasking tests, no regressions on EPCC.
+static void __kmp_x86_pause(void) { _mm_delay_32(300); }
 #else
 static void __kmp_x86_pause(void) { _mm_pause(); }
 #endif
@@ -1076,16 +1080,16 @@
     KMP_CPU_PAUSE();                                                           \
     (count) -= 2;                                                              \
     if (!(count)) {                                                            \
-      KMP_YIELD(cond);                                                         \
+      __kmp_yield(cond);                                                       \
       (count) = __kmp_yield_next;                                              \
     }                                                                          \
   }
 #define KMP_YIELD_SPIN(count)                                                  \
   {                                                                            \
     KMP_CPU_PAUSE();                                                           \
     (count) -= 2;                                                              \
     if (!(count)) {                                                            \
-      KMP_YIELD(1);                                                            \
+      __kmp_yield(1);                                                          \
       (count) = __kmp_yield_next;                                              \
     }                                                                          \
   }
Index: openmp/trunk/runtime/src/kmp_wait_release.h
===================================================================
--- openmp/trunk/runtime/src/kmp_wait_release.h
+++ openmp/trunk/runtime/src/kmp_wait_release.h
@@ -47,7 +47,7 @@
  */
 template <typename P> class kmp_flag {
   volatile P
-    *loc; /**< Pointer to the flag storage that is modified by another thread
+      *loc; /**< Pointer to the flag storage that is modified by another thread
              */
   flag_type t; /**< "Type" of the flag in loc */
 public:
@@ -225,11 +225,14 @@
 
     // If we are oversubscribed, or have waited a bit (and
     // KMP_LIBRARY=throughput), then yield
-    KMP_YIELD(oversubscribed);
     // TODO: Should it be number of cores instead of thread contexts? Like:
     // KMP_YIELD(TCR_4(__kmp_nth) > __kmp_ncores);
     // Need performance improvement data to make the change...
-    KMP_YIELD_SPIN(spins);
+    if (oversubscribed) {
+      KMP_YIELD(1);
+    } else {
+      KMP_YIELD_SPIN(spins);
+    }
     // Check if this thread was transferred from a team
     // to the thread pool (or vice-versa) while spinning.
     in_pool = !!TCR_4(this_thr->th.th_in_pool);


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