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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

llvm-svn: 293312
This commit is contained in:
Jonathan Peyton 2017-01-27 17:54:31 +00:00
parent 3b34a9b5d9
commit 2208a85101
3 changed files with 27 additions and 21 deletions
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18
openmp/runtime/src/kmp.h
View File

@ -889,6 +889,20 @@ extern int __kmp_place_num_threads_per_core;
#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_info {
/* 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

12
openmp/runtime/src/kmp_barrier.cpp
View File

@ -1130,8 +1130,10 @@ __kmp_barrier(enum barrier_type bt, int gtid, int is_split, size_t reduce_size,
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

18
openmp/runtime/src/kmp_wait_release.h
View File

@ -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, C *flag, int final_spin
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
}