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Change task stealing to always get task from head of victim's deque. 

Differential Revision: https://reviews.llvm.org/D26187

llvm-svn: 285833
This commit is contained in:
Andrey Churbanov 2016-11-02 16:45:25 +00:00
parent 06ac79c210
commit 753fa0468c
1 changed files with 8 additions and 13 deletions
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21
openmp/runtime/src/kmp_tasking.c
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@ -1782,18 +1782,10 @@ __kmp_steal_task( kmp_info_t *victim, kmp_int32 gtid, kmp_task_team_t *task_team
KMP_DEBUG_ASSERT( victim_td -> td.td_deque != NULL );
if ( !is_constrained ) {
taskdata = victim_td -> td.td_deque[ victim_td -> td.td_deque_head ];
KMP_ASSERT(taskdata);
// Bump head pointer and Wrap.
victim_td -> td.td_deque_head = ( victim_td -> td.td_deque_head + 1 ) & TASK_DEQUE_MASK(victim_td->td);
} else {
// While we have postponed tasks let's steal from tail of the deque (smaller tasks)
kmp_int32 tail = ( victim_td -> td.td_deque_tail - 1 ) & TASK_DEQUE_MASK(victim_td->td); // Wrap index.
taskdata = victim_td -> td.td_deque[ tail ];
KMP_ASSERT(taskdata);
taskdata = victim_td->td.td_deque[victim_td->td.td_deque_head];
if ( is_constrained ) {
// we need to check if the candidate obeys task scheduling constraint:
// only child of current task can be scheduled
// only descendant of current task can be scheduled
kmp_taskdata_t * current = __kmp_threads[ gtid ]->th.th_current_task;
kmp_int32 level = current->td_level;
kmp_taskdata_t * parent = taskdata->td_parent;
@ -1802,7 +1794,9 @@ __kmp_steal_task( kmp_info_t *victim, kmp_int32 gtid, kmp_task_team_t *task_team
KMP_DEBUG_ASSERT(parent != NULL);
}
if ( parent != current ) {
// If the tail task is not a descendant of the current task then do not steal it.
// If the head task is not a descendant of the current task then do not
// steal it. No other task in victim's deque can be a descendant of the
// current task.
__kmp_release_bootstrap_lock( & victim_td -> td.td_deque_lock );
KA_TRACE(10, ("__kmp_steal_task(exit #2): T#%d could not steal from T#%d: task_team=%p "
"ntasks=%d head=%u tail=%u\n",
@ -1811,8 +1805,9 @@ __kmp_steal_task( kmp_info_t *victim, kmp_int32 gtid, kmp_task_team_t *task_team
victim_td->td.td_deque_head, victim_td->td.td_deque_tail) );
return NULL;
}
victim_td -> td.td_deque_tail = tail;
}
// Bump head pointer and Wrap.
victim_td->td.td_deque_head = (victim_td->td.td_deque_head + 1) & TASK_DEQUE_MASK(victim_td->td);
if (*thread_finished) {
// We need to un-mark this victim as a finished victim. This must be done before
// releasing the lock, or else other threads (starting with the master victim)