tasklet: Add lock-free exit path from do_tasklet() when no work to do.

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/xen/common/tasklet.c b/xen/common/tasklet.c
index 05665ebc5d..e2109770ad 100644
--- a/xen/common/tasklet.c
+++ b/xen/common/tasklet.c
@@ -60,9 +60,12 @@ void do_tasklet(void)
     struct list_head *list = &per_cpu(tasklet_list, cpu);
     struct tasklet *t;
 
+    if ( likely(list_empty(list)) )
+        return;
+
     spin_lock_irq(&tasklet_lock);
 
-    if ( list_empty(list) )
+    if ( unlikely(list_empty(list)) )
     {
         spin_unlock_irq(&tasklet_lock);
         return;