perf: Remove 64-bit alignment padding from perf_event_context

Reorder perf_event_context to remove 8 bytes of 64 bit alignment padding
shrinking its size to 192 bytes, allowing it to fit into a smaller slab
and use one fewer cache lines.
Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1307460819.1950.5.camel@castor.rskSigned-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/perf_event.h

@@ -894,8 +894,8 @@ struct perf_event_context {
 	u64				parent_gen;
 	u64				generation;
 	int				pin_count;
-	struct rcu_head			rcu_head;
 	int				nr_cgroups; /* cgroup events present */
+	struct rcu_head			rcu_head;
 };
 
 /*