[RFC PATCH 1/2] membarrier: speed up single-threaded private cmd

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

Single-threaded processes don't need to issue barriers, since the
thread's current CPU is the only one that matters.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Andrew Hunter <ahh@google.com>
CC: Maged Michael <maged.michael@gmail.com>
CC: gromer@google.com
CC: Avi Kivity <avi@scylladb.com>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Paul Mackerras <paulus@samba.org>
CC: Michael Ellerman <mpe@ellerman.id.au>
CC: Dave Watson <davejwatson@fb.com>
---
 kernel/sched/membarrier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index a92fddc22747..7eec6914d2d2 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -39,7 +39,7 @@ static void membarrier_private_expedited(void)
 	bool fallback = false;
 	cpumask_var_t tmpmask;
 
-	if (num_online_cpus() == 1)
+	if (num_online_cpus() == 1 || get_nr_threads(current) == 1)
 		return;
 
 	/*
-- 
2.11.0