[tip: sched/core] sched/topology: Mark SD_PREFER_SIBLING as SDF_NEEDS_GROUPS

[tip-bot2 for Valentin Schneider]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     3a6712c7685352a5d71eaf459a4fddfc3589f018
Gitweb:        https://git.kernel.org/tip/3a6712c7685352a5d71eaf459a4fddfc3589f018
Author:        Valentin Schneider <valentin.schneider@xxxxxxx>
AuthorDate:    Mon, 17 Aug 2020 12:29:57 +01:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 19 Aug 2020 10:49:49 +02:00

sched/topology: Mark SD_PREFER_SIBLING as SDF_NEEDS_GROUPS

SD_PREFER_SIBLING is currently considered in sd_parent_degenerate() but not
in sd_degenerate(). It too hinges on load balancing, and thus won't have
any effect when set on a domain with a single group. Add it to
SD_DEGENERATE_GROUPS_MASK.

Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Link: https://lore.kernel.org/r/20200817113003.20802-12-valentin.schneider@xxxxxxx
---
 include/linux/sched/sd_flags.h | 4 +++-
 kernel/sched/topology.c        | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched/sd_flags.h b/include/linux/sched/sd_flags.h
index 40ad0d5..d28fe67 100644
--- a/include/linux/sched/sd_flags.h
+++ b/include/linux/sched/sd_flags.h
@@ -131,8 +131,10 @@ SD_FLAG(SD_ASYM_PACKING, SDF_SHARED_CHILD)
  *
  * Set up until domains start spanning NUMA nodes. Close to being a SHARED_CHILD
  * flag, but cleared below domains with SD_ASYM_CPUCAPACITY.
+ *
+ * NEEDS_GROUPS: Load balancing flag.
  */
-SD_FLAG(SD_PREFER_SIBLING, 0)
+SD_FLAG(SD_PREFER_SIBLING, SDF_NEEDS_GROUPS)
 
 /*
  * sched_groups of this level overlap
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index f36ed96..c674aaa 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -184,7 +184,7 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
 
 	/* Flags needing groups don't count if only 1 group in parent */
 	if (parent->groups == parent->groups->next)
-		pflags &= ~(SD_DEGENERATE_GROUPS_MASK | SD_PREFER_SIBLING);
+		pflags &= ~SD_DEGENERATE_GROUPS_MASK;
 
 	if (~cflags & pflags)
 		return 0;