sched: Fix select_idle_sibling() regression in selecting an idle SMT sibling

Mike Galbraith reported that this recent commit:

   commit 4dcfe1025b513c2c1da5bf5586adb0e80148f612
   Author: Peter Zijlstra <[email protected]>
   Date:   Thu Nov 10 13:01:10 2011 +0100

       sched: Avoid SMT siblings in select_idle_sibling() if possible

stopped selecting an idle SMT sibling when there are no idle
cores in a single socket system.

Intent of the select_idle_sibling() was to fallback to an idle
SMT sibling, if it fails to identify an idle core. But this
fallback was not happening on systems where all the scheduler
domains had `SD_SHARE_PKG_RESOURCES' flag set.

Fix it. Slightly bigger patch of cleaning all these goto's etc
is queued up for the next release.

Reported-by: Mike Galbraith <[email protected]>
Reported-by: Alex Shi <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: Suresh Siddha <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 8 insertions, 6 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index a78ed2736ba7..8a39fa3e3c6c 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2352,13 +2352,11 @@ again:
 		if (!smt && (sd->flags & SD_SHARE_CPUPOWER))
 			continue;
 
-		if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {
-			if (!smt) {
-				smt = 1;
-				goto again;
-			}
+		if (smt && !(sd->flags & SD_SHARE_CPUPOWER))
+			break;
+
+		if (!(sd->flags & SD_SHARE_PKG_RESOURCES))
 			break;
-		}
 
 		sg = sd->groups;
 		do {
@@ -2378,6 +2376,10 @@ next:
 			sg = sg->next;
 		} while (sg != sd->groups);
 	}
+	if (!smt) {
+		smt = 1;
+		goto again;
+	}
 done:
 	rcu_read_unlock();