[PATCH] sched/fair: Fix kernel build warning in test_idle_cores() for !SMT NUMA

[Mel Gorman]

Building against tip/sched/core as of as ff7db0bf24db ("sched/numa: Prefer
using an idle CPU as a migration target instead of comparing tasks") with
the arm64 defconfig (which doesn't have CONFIG_SCHED_SMT set) leads to:

  kernel/sched/fair.c:1525:20: warning: â??test_idle_coresâ?? declared â??staticâ?? but never defined [-Wunused-function]
   static inline bool test_idle_cores(int cpu, bool def);
		      ^~~~~~~~~~~~~~~

Rather than define it in its own CONFIG_SCHED_SMT #define island, bunch it
up with test_idle_cores().

Fixes: ff7db0bf24db ("sched/numa: Prefer using an idle CPU as a migration target instead of comparing tasks")
[mgorman@xxxxxxxxxxxxxxxxxxx: Edit changelog, minor style change]
Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
---
 kernel/sched/fair.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fcc968669aea..10f9e6729fcf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1520,9 +1520,6 @@ static inline bool is_core_idle(int cpu)
 	return true;
 }
 
-/* Forward declarations of select_idle_sibling helpers */
-static inline bool test_idle_cores(int cpu, bool def);
-
 struct task_numa_env {
 	struct task_struct *p;
 
@@ -1558,9 +1555,11 @@ numa_type numa_classify(unsigned int imbalance_pct,
 	return node_fully_busy;
 }
 
+#ifdef CONFIG_SCHED_SMT
+/* Forward declarations of select_idle_sibling helpers */
+static inline bool test_idle_cores(int cpu, bool def);
 static inline int numa_idle_core(int idle_core, int cpu)
 {
-#ifdef CONFIG_SCHED_SMT
 	if (!static_branch_likely(&sched_smt_present) ||
 	    idle_core >= 0 || !test_idle_cores(cpu, false))
 		return idle_core;
@@ -1571,10 +1570,15 @@ static inline int numa_idle_core(int idle_core, int cpu)
 	 */
 	if (is_core_idle(cpu))
 		idle_core = cpu;
-#endif
 
 	return idle_core;
 }
+#else
+static inline int numa_idle_core(int idle_core, int cpu)
+{
+	return idle_core;
+}
+#endif
 
 /*
  * Gather all necessary information to make NUMA balancing placement