sched: only balance our RT tasks within our domain

We move the rt-overload data as the first global to per-domain
reclassification.  This limits the scope of overload related cache-line
bouncing to stay with a specified partition instead of affecting all
cpus in the system.

Finally, we limit the scope of find_lowest_cpu searches to the domain
instead of the entire system.  Note that we would always respect domain
boundaries even without this patch, but we first would scan potentially
all cpus before whittling the list down.  Now we can avoid looking at
RQs that are out of scope, again reducing cache-line hits.

Note: In some cases, task->cpus_allowed will effectively reduce our search
to within our domain.  However, I believe there are cases where the
cpus_allowed mask may be all ones and therefore we err on the side of
caution.  If it can be optimized later, so be it.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
CC: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 34b7d721d735..35ef06c99214 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -365,6 +365,13 @@ struct root_domain {
 	atomic_t refcount;
 	cpumask_t span;
 	cpumask_t online;
+
+        /*
+	 * The "RT overload" flag: it gets set if a CPU has more than
+	 * one runnable RT task.
+	 */
+	cpumask_t rto_mask;
+	atomic_t  rto_count;
 };
 
 static struct root_domain def_root_domain;