sched/fair: Default to false in test_idle_cores()

It's uncertain whether idle cores exist or not if shared sched-
domains are not ready, so returning "no idle cores" usually
makes sense.

While __update_idle_core() is an exception, it checks status
of this core and set hint to shared sched-domain if necessary.
So the whole logic of this function depends on the existence
of shared sched-domain, and can certainly bail out early if
it is not available.

It's somehow a little tricky, and as Josh suggested that it
should be transient while the domain isn't ready. So remove
the self-defined default value to make things more clearer.

Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Don <joshdon@google.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lore.kernel.org/r/20220907112000.1854-5-wuyun.abel@bytedance.com

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 03ce65068333d9aa49a711691e6186c3a314ffc2..23b020c3d3a030d66fda4db26d77f35a64ebe2ed 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1588,11 +1588,11 @@ numa_type numa_classify(unsigned int imbalance_pct,
 
 #ifdef CONFIG_SCHED_SMT
 /* Forward declarations of select_idle_sibling helpers */
-static inline bool test_idle_cores(int cpu, bool def);
+static inline bool test_idle_cores(int cpu);
 static inline int numa_idle_core(int idle_core, int cpu)
 {
        if (!static_branch_likely(&sched_smt_present) ||
-           idle_core >= 0 || !test_idle_cores(cpu, false))
+           idle_core >= 0 || !test_idle_cores(cpu))
                return idle_core;
 
        /*
@@ -6271,7 +6271,7 @@ static inline void set_idle_cores(int cpu, int val)
                WRITE_ONCE(sds->has_idle_cores, val);
 }
 
-static inline bool test_idle_cores(int cpu, bool def)
+static inline bool test_idle_cores(int cpu)
 {
        struct sched_domain_shared *sds;
 
@@ -6279,7 +6279,7 @@ static inline bool test_idle_cores(int cpu, bool def)
        if (sds)
                return READ_ONCE(sds->has_idle_cores);
 
-       return def;
+       return false;
 }
 
 /*
@@ -6295,7 +6295,7 @@ void __update_idle_core(struct rq *rq)
        int cpu;
 
        rcu_read_lock();
-       if (test_idle_cores(core, true))
+       if (test_idle_cores(core))
                goto unlock;
 
        for_each_cpu(cpu, cpu_smt_mask(core)) {
@@ -6367,9 +6367,9 @@ static inline void set_idle_cores(int cpu, int val)
 {
 }
 
-static inline bool test_idle_cores(int cpu, bool def)
+static inline bool test_idle_cores(int cpu)
 {
-       return def;
+       return false;
 }
 
 static inline int select_idle_core(struct task_struct *p, int core, struct cpumask *cpus, int *idle_cpu)
@@ -6608,7 +6608,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
                return target;
 
        if (sched_smt_active()) {
-               has_idle_core = test_idle_cores(target, false);
+               has_idle_core = test_idle_cores(target);
 
                if (!has_idle_core && cpus_share_cache(prev, target)) {
                        i = select_idle_smt(p, prev);