[PATCH v4 08/12] sched/topology: Check SDF_SHARED_CHILD in highest_flag_domain()

[Ricardo Neri]

Do not assume that all the children of a scheduling domain have a given
flag. Check whether it has the SDF_SHARED_CHILD meta flag.

Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Ionela Voinescu <ionela.voinescu@xxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Tim C. Chen <tim.c.chen@xxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Suggested-by: Ionela Voinescu <ionela.voinescu@xxxxxxx>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
Changes since v3:
 * Introduced this patch.

Changes since v2:
 * N/A

Changes since v1:
 * N/A
---
 kernel/sched/sched.h | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 060616944d7a..70abce91b549 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1772,6 +1772,13 @@ queue_balance_callback(struct rq *rq,
 	for (__sd = rcu_dereference_check_sched_domain(cpu_rq(cpu)->sd); \
 			__sd; __sd = __sd->parent)
 
+/* A mask of all the SD flags that have the SDF_SHARED_CHILD metaflag */
+#define SD_FLAG(name, mflags) (name * !!((mflags) & SDF_SHARED_CHILD)) |
+static const unsigned int SD_SHARED_CHILD_MASK =
+#include <linux/sched/sd_flags.h>
+0;
+#undef SD_FLAG
+
 /**
  * highest_flag_domain - Return highest sched_domain containing flag.
  * @cpu:	The CPU whose highest level of sched domain is to
@@ -1779,16 +1786,25 @@ queue_balance_callback(struct rq *rq,
  * @flag:	The flag to check for the highest sched_domain
  *		for the given CPU.
  *
- * Returns the highest sched_domain of a CPU which contains the given flag.
+ * Returns the highest sched_domain of a CPU which contains @flag. If @flag has
+ * the SDF_SHARED_CHILD metaflag, all the children domains also have @flag.
  */
 static inline struct sched_domain *highest_flag_domain(int cpu, int flag)
 {
 	struct sched_domain *sd, *hsd = NULL;
 
 	for_each_domain(cpu, sd) {
-		if (!(sd->flags & flag))
+		if (sd->flags & flag) {
+			hsd = sd;
+			continue;
+		}
+
+		/*
+		 * Stop the search if @flag is known to be shared at lower
+		 * levels. It will not be found further up.
+		 */
+		if (flag & SD_SHARED_CHILD_MASK)
 			break;
-		hsd = sd;
 	}
 
 	return hsd;
-- 
2.25.1