[tip: sched/core] sched/fair: Clear SMT siblings after determining the core is not idle

[tip-bot2 for Mel Gorman]

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

Commit-ID:     82b738de57d571cd366d89e75b5fd60f3060852b
Gitweb:        https://git.kernel.org/tip/82b738de57d571cd366d89e75b5fd60f3060852b
Author:        Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
AuthorDate:    Mon, 30 Nov 2020 14:40:20 
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 03 Dec 2020 10:00:36 +01:00

sched/fair: Clear SMT siblings after determining the core is not idle

The clearing of SMT siblings from the SIS mask before checking for an idle
core is a small but unnecessary cost. Defer the clearing of the siblings
until the scan moves to the next potential target. The cost of this was
not measured as it is borderline noise but it should be self-evident.

Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20201130144020.GS3371@xxxxxxxxxxxxxxxxxxx
---
 kernel/sched/fair.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f5dceda..efac224 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6086,10 +6086,11 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int 
 				break;
 			}
 		}
-		cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
 
 		if (idle)
 			return core;
+
+		cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
 	}
 
 	/*