ck_barrier: Just pass-through tournament barrier with only one participating thread.

include/ck_barrier.h

@@ -121,6 +121,7 @@ typedef struct ck_barrier_tournament_round ck_barrier_tournament_round_t;
 
 struct ck_barrier_tournament {
 	unsigned int tid;
+	unsigned int size;
 	struct ck_barrier_tournament_round **rounds;
 };
 typedef struct ck_barrier_tournament ck_barrier_tournament_t;

src/ck_barrier_tournament.c

@@ -64,7 +64,7 @@ ck_barrier_tournament_init(struct ck_barrier_tournament *barrier,
 	unsigned int i, k, size, twok, twokm1, imod2k;
 
 	ck_pr_store_uint(&barrier->tid, 0);
-	size = ck_barrier_tournament_size(nthr);
+	barrier->size = size = ck_barrier_tournament_size(nthr);
 
 	for (i = 0; i < nthr; ++i) {
 		/* The first role is always CK_BARRIER_TOURNAMENT_DROPOUT. */
@@ -112,6 +112,9 @@ ck_barrier_tournament(struct ck_barrier_tournament *barrier,
 	struct ck_barrier_tournament_round **rounds = ck_pr_load_ptr(&barrier->rounds);
 	int round = 1;
 
+	if (barrier->size == 1)
+		return;
+
 	for (;; ++round) {
 		switch (rounds[state->vpid][round].role) {
 		case CK_BARRIER_TOURNAMENT_BYE: