[Xen-changelog] [xen-unstable] tasklet: Add lock-free exit path from do_tasklet() when no work to do.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1271770373 -3600
# Node ID dbf0fd95180f97bdf403ada605400723e4e8563d
# Parent  b2c56f91da8d34e4daf4cceb1fc8a70a33656ae2
tasklet: Add lock-free exit path from do_tasklet() when no work to do.

Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
---
 xen/common/tasklet.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletion(-)

diff -r b2c56f91da8d -r dbf0fd95180f xen/common/tasklet.c
--- a/xen/common/tasklet.c      Tue Apr 20 07:54:47 2010 +0100
+++ b/xen/common/tasklet.c      Tue Apr 20 14:32:53 2010 +0100
@@ -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;

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