[llvm-branch-commits] [openmp] 4fe17ad - [OpenMP] Fix hierarchical barrier

[Nawrin Sultana via llvm-branch-commits]

Author: Terry Wilmarth
Date: 2021-01-13T10:22:57-06:00
New Revision: 4fe17ada55ade9b77e18521dae0985cb4a88f6c4

URL: https://github.com/llvm/llvm-project/commit/4fe17ada55ade9b77e18521dae0985cb4a88f6c4
DIFF: https://github.com/llvm/llvm-project/commit/4fe17ada55ade9b77e18521dae0985cb4a88f6c4.diff

LOG: [OpenMP] Fix hierarchical barrier

Hierarchical barrier is an experimental barrier algorithm that uses aspects
of machine hierarchy to define the barrier tree structure. This patch fixes
offset calculation in hierarchical barrier. The offset is used to store info
on a flag about sleeping threads waiting on a location stored in the flag.
This commit also fixes a potential deadlock in hierarchical barrier when
using infinite blocktime by adjusting the offset value of leaf kids so that
it matches the value of leaf state. It also adds testing of default barriers
with infinite blocktime, and also tests hierarchical barrier algorithm with
both default and infinite blocktime.

Patch by Terry Wilmarth and Nawrin Sultana.

Differential Revision: https://reviews.llvm.org/D94241

Added: 
    

Modified: 
    openmp/runtime/src/kmp_barrier.cpp
    openmp/runtime/test/barrier/omp_barrier.c

Removed: 
    


################################################################################
diff  --git a/openmp/runtime/src/kmp_barrier.cpp b/openmp/runtime/src/kmp_barrier.cpp
index 1fef5c9936ff..4da2d0bd5220 100644
--- a/openmp/runtime/src/kmp_barrier.cpp
+++ b/openmp/runtime/src/kmp_barrier.cpp
@@ -828,8 +828,8 @@ static bool __kmp_init_hierarchical_barrier_thread(enum barrier_type bt,
           thr_bar->parent_tid = 0;
           thr_bar->my_level = d;
           break;
-        } else if ((rem = tid % thr_bar->skip_per_level[d + 1]) !=
-                   0) { // TODO: can we make this op faster?
+        } else if ((rem = tid % thr_bar->skip_per_level[d + 1]) != 0) {
+          // TODO: can we make the above op faster?
           // thread is not a subtree root at next level, so this is max
           thr_bar->parent_tid = tid - rem;
           thr_bar->my_level = d;
@@ -838,7 +838,9 @@ static bool __kmp_init_hierarchical_barrier_thread(enum barrier_type bt,
         ++d;
       }
     }
-    __kmp_type_convert(7 - (tid - thr_bar->parent_tid - 1), &(thr_bar->offset));
+    __kmp_type_convert(7 - ((tid - thr_bar->parent_tid) /
+                            (thr_bar->skip_per_level[thr_bar->my_level])),
+                       &(thr_bar->offset));
     thr_bar->old_tid = tid;
     thr_bar->wait_flag = KMP_BARRIER_NOT_WAITING;
     thr_bar->team = team;
@@ -1029,7 +1031,8 @@ static void __kmp_hierarchical_barrier_gather(
     } else {
       // Leaf does special release on "offset" bits of parent's b_arrived flag
       thr_bar->b_arrived = team->t.t_bar[bt].b_arrived + KMP_BARRIER_STATE_BUMP;
-      kmp_flag_oncore flag(&thr_bar->parent_bar->b_arrived, thr_bar->offset);
+      kmp_flag_oncore flag(&thr_bar->parent_bar->b_arrived,
+                           thr_bar->offset + 1);
       flag.set_waiter(other_threads[thr_bar->parent_tid]);
       flag.release();
     }
@@ -1078,7 +1081,7 @@ static void __kmp_hierarchical_barrier_release(
       // Wait on my "offset" bits on parent's b_go flag
       thr_bar->wait_flag = KMP_BARRIER_PARENT_FLAG;
       kmp_flag_oncore flag(&thr_bar->parent_bar->b_go, KMP_BARRIER_STATE_BUMP,
-                           thr_bar->offset, bt,
+                           thr_bar->offset + 1, bt,
                            this_thr USE_ITT_BUILD_ARG(itt_sync_obj));
       flag.wait(this_thr, TRUE);
       if (thr_bar->wait_flag ==
@@ -1087,7 +1090,7 @@ static void __kmp_hierarchical_barrier_release(
               KMP_INIT_BARRIER_STATE); // Reset my b_go flag for next time
       } else { // Reset my bits on parent's b_go flag
         (RCAST(volatile char *,
-               &(thr_bar->parent_bar->b_go)))[thr_bar->offset] = 0;
+               &(thr_bar->parent_bar->b_go)))[thr_bar->offset + 1] = 0;
       }
     }
     thr_bar->wait_flag = KMP_BARRIER_NOT_WAITING;

diff  --git a/openmp/runtime/test/barrier/omp_barrier.c b/openmp/runtime/test/barrier/omp_barrier.c
index a3fb06086a3f..3da70db92890 100644
--- a/openmp/runtime/test/barrier/omp_barrier.c
+++ b/openmp/runtime/test/barrier/omp_barrier.c
@@ -1,4 +1,7 @@
 // RUN: %libomp-compile-and-run
+// RUN: %libomp-compile && env KMP_BLOCKTIME=infinite %libomp-run
+// RUN: %libomp-compile && env KMP_PLAIN_BARRIER_PATTERN='hierarchical,hierarchical' KMP_FORKJOIN_BARRIER_PATTERN='hierarchical,hierarchical' %libomp-run
+// RUN: %libomp-compile && env KMP_BLOCKTIME=infinite KMP_PLAIN_BARRIER_PATTERN='hierarchical,hierarchical' KMP_FORKJOIN_BARRIER_PATTERN='hierarchical,hierarchical' %libomp-run
 #include <stdio.h>
 #include "omp_testsuite.h"
 #include "omp_my_sleep.h"