[Openmp-commits] [openmp] r293312 - Fix performance issue incurred by removing monitor thread.

[Jonathan Peyton via Openmp-commits]

Author: jlpeyton
Date: Fri Jan 27 11:54:31 2017
New Revision: 293312

URL: http://llvm.org/viewvc/llvm-project?rev=293312&view=rev
Log:
Fix performance issue incurred by removing monitor thread.

When the monitor thread is used, most threads in the team directly go to
sleep if the copy of bt_intervals/bt_set is not available in the cache,
and this happens at least once per thread in the wait function, making the
overall performance slightly better.
This change tries to mimic this behavior by using the bt_intervals cache,
which simply keeps the blocktime interval in terms of the platform-dependent
ticks or nanoseconds.

Patch by Hansang Bae

Differential Revision: https://reviews.llvm.org/D28906

Modified:
    openmp/trunk/runtime/src/kmp.h
    openmp/trunk/runtime/src/kmp_barrier.cpp
    openmp/trunk/runtime/src/kmp_wait_release.h

Modified: openmp/trunk/runtime/src/kmp.h
URL: http://llvm.org/viewvc/llvm-project/openmp/trunk/runtime/src/kmp.h?rev=293312&r1=293311&r2=293312&view=diff
==============================================================================
--- openmp/trunk/runtime/src/kmp.h (original)
+++ openmp/trunk/runtime/src/kmp.h Fri Jan 27 11:54:31 2017
@@ -889,6 +889,20 @@ extern int __kmp_place_num_threads_per_c
 #define KMP_INTERVALS_FROM_BLOCKTIME(blocktime, monitor_wakeups)  \
                                  ( ( (blocktime) + (KMP_BLOCKTIME_MULTIPLIER / (monitor_wakeups)) - 1 ) /  \
                                    (KMP_BLOCKTIME_MULTIPLIER / (monitor_wakeups)) )
+#else
+# if KMP_OS_UNIX && (KMP_ARCH_X86 || KMP_ARCH_X86_64)
+   // HW TSC is used to reduce overhead (clock tick instead of nanosecond).
+   extern double __kmp_ticks_per_nsec;
+#  define KMP_NOW() __kmp_hardware_timestamp()
+#  define KMP_BLOCKTIME_INTERVAL() (__kmp_dflt_blocktime * KMP_USEC_PER_SEC * __kmp_ticks_per_nsec)
+#  define KMP_BLOCKING(goal, count) ((goal) > KMP_NOW())
+# else
+   // System time is retrieved sporadically while blocking.
+   extern kmp_uint64 __kmp_now_nsec();
+#  define KMP_NOW() __kmp_now_nsec()
+#  define KMP_BLOCKTIME_INTERVAL() (__kmp_dflt_blocktime * KMP_USEC_PER_SEC)
+#  define KMP_BLOCKING(goal, count) ((count) % 1000 != 0 || (goal) > KMP_NOW())
+# endif
 #endif // KMP_USE_MONITOR
 
 #define KMP_MIN_STATSCOLS       40
@@ -2220,8 +2234,10 @@ typedef struct KMP_ALIGN_CACHE kmp_base_
     /* to exist (from the POV of worker threads).                            */
 #if KMP_USE_MONITOR
     int               th_team_bt_intervals;
-#endif
     int               th_team_bt_set;
+#else
+    kmp_uint64        th_team_bt_intervals;
+#endif
 
 
 #if KMP_AFFINITY_SUPPORTED

Modified: openmp/trunk/runtime/src/kmp_barrier.cpp
URL: http://llvm.org/viewvc/llvm-project/openmp/trunk/runtime/src/kmp_barrier.cpp?rev=293312&r1=293311&r2=293312&view=diff
==============================================================================
--- openmp/trunk/runtime/src/kmp_barrier.cpp (original)
+++ openmp/trunk/runtime/src/kmp_barrier.cpp Fri Jan 27 11:54:31 2017
@@ -1130,8 +1130,10 @@ __kmp_barrier(enum barrier_type bt, int
         if (__kmp_dflt_blocktime != KMP_MAX_BLOCKTIME) {
 #if KMP_USE_MONITOR
             this_thr->th.th_team_bt_intervals = team->t.t_implicit_task_taskdata[tid].td_icvs.bt_intervals;
-#endif
             this_thr->th.th_team_bt_set = team->t.t_implicit_task_taskdata[tid].td_icvs.bt_set;
+#else
+            this_thr->th.th_team_bt_intervals = KMP_BLOCKTIME_INTERVAL();
+#endif
         }
 
 #if USE_ITT_BUILD
@@ -1453,8 +1455,10 @@ __kmp_join_barrier(int gtid)
     if (__kmp_dflt_blocktime != KMP_MAX_BLOCKTIME) {
 #if KMP_USE_MONITOR
         this_thr->th.th_team_bt_intervals = team->t.t_implicit_task_taskdata[tid].td_icvs.bt_intervals;
-#endif
         this_thr->th.th_team_bt_set = team->t.t_implicit_task_taskdata[tid].td_icvs.bt_set;
+#else
+        this_thr->th.th_team_bt_intervals = KMP_BLOCKTIME_INTERVAL();
+#endif
     }
 
 #if USE_ITT_BUILD
@@ -1644,8 +1648,10 @@ __kmp_fork_barrier(int gtid, int tid)
         if (__kmp_dflt_blocktime != KMP_MAX_BLOCKTIME) {
 #if KMP_USE_MONITOR
             this_thr->th.th_team_bt_intervals = team->t.t_implicit_task_taskdata[tid].td_icvs.bt_intervals;
-#endif
             this_thr->th.th_team_bt_set = team->t.t_implicit_task_taskdata[tid].td_icvs.bt_set;
+#else
+            this_thr->th.th_team_bt_intervals = KMP_BLOCKTIME_INTERVAL();
+#endif
         }
     } // master
 

Modified: openmp/trunk/runtime/src/kmp_wait_release.h
URL: http://llvm.org/viewvc/llvm-project/openmp/trunk/runtime/src/kmp_wait_release.h?rev=293312&r1=293311&r2=293312&view=diff
==============================================================================
--- openmp/trunk/runtime/src/kmp_wait_release.h (original)
+++ openmp/trunk/runtime/src/kmp_wait_release.h Fri Jan 27 11:54:31 2017
@@ -84,22 +84,6 @@ class kmp_flag {
     */
 };
 
-#if ! KMP_USE_MONITOR
-# if KMP_OS_UNIX && (KMP_ARCH_X86 || KMP_ARCH_X86_64)
-   // HW TSC is used to reduce overhead (clock tick instead of nanosecond).
-   extern double __kmp_ticks_per_nsec;
-#  define KMP_NOW() __kmp_hardware_timestamp()
-#  define KMP_BLOCKTIME_INTERVAL() (__kmp_dflt_blocktime * KMP_USEC_PER_SEC * __kmp_ticks_per_nsec)
-#  define KMP_BLOCKING(goal, count) ((goal) > KMP_NOW())
-# else
-   // System time is retrieved sporadically while blocking.
-   extern kmp_uint64 __kmp_now_nsec();
-#  define KMP_NOW() __kmp_now_nsec()
-#  define KMP_BLOCKTIME_INTERVAL() (__kmp_dflt_blocktime * KMP_USEC_PER_SEC)
-#  define KMP_BLOCKING(goal, count) ((count) % 1000 != 0 || (goal) > KMP_NOW())
-# endif
-#endif
-
 /* Spin wait loop that first does pause, then yield, then sleep. A thread that calls __kmp_wait_*
    must make certain that another thread calls __kmp_release to wake it back up to prevent deadlocks!  */
 template <class C>
@@ -187,7 +171,7 @@ __kmp_wait_template(kmp_info_t *this_thr
                       th_gtid, __kmp_global.g.g_time.dt.t_value, hibernate,
                       hibernate - __kmp_global.g.g_time.dt.t_value));
 #else
-        hibernate_goal = KMP_NOW() + KMP_BLOCKTIME_INTERVAL();
+        hibernate_goal = KMP_NOW() + this_thr->th.th_team_bt_intervals;
         poll_count = 0;
 #endif // KMP_USE_MONITOR
     }