sched: Simplify ifdeffery around cpu_smt_mask

Now, that cpu_smt_mask is defined as cpumask_of(cpu) for
CONFIG_SCHED_SMT=n, it is possible to get rid of the ifdeffery.

Effectively,
 - This makes sched_smt_present is defined always

 - cpumask_weight(cpumask_of(cpu)) == 1. So sched_smt_present_inc/dec
   will never enable the sched_smt_present. Which is expected.

 - Paths that were compile-time eliminated become runtime guarded
   using static keys.

 - Defines set_idle_cores, test_idle_cores, etc which could likely benefit
   the CONFIG_SCHED_SMT=n systems to use the same optimizations within the
   LLC at wakeups.

 - This will expose sched_smt_present symbol for CONFIG_SCHED_SMT=n.
   Likely not a concern.

 - There is a bloat of code CONFIG_SCHED_SMT=n. (NR_CPUS=2048)
   add/remove: 24/18 grow/shrink: 26/28 up/down: 6396/-3188 (3208)
   Total: Before=30629880, After=30633088, chg +0.01%

 - No code bloat for CONFIG_SCHED_SMT=y, which is expected.

 - Add comments around stop_core_cpuslocked on why ifdefs are not
   removed.

 - This leaves the remaining uses of CONFIG_SCHED_SMT mainly for
   topology building bits which has a policy based decision.

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://patch.msgid.link/20260515172456.542799-3-sshegde@linux.ibm.com

5 files changed, 0 insertions, 55 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b905805bbcbe..3ae5f19c1b7e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8612,18 +8612,14 @@ static void cpuset_cpu_inactive(unsigned int cpu)
 
 static inline void sched_smt_present_inc(int cpu)
 {
-#ifdef CONFIG_SCHED_SMT
 	if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
 		static_branch_inc_cpuslocked(&sched_smt_present);
-#endif
 }
 
 static inline void sched_smt_present_dec(int cpu)
 {
-#ifdef CONFIG_SCHED_SMT
 	if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
 		static_branch_dec_cpuslocked(&sched_smt_present);
-#endif
 }
 
 int sched_cpu_activate(unsigned int cpu)
@@ -8711,9 +8707,7 @@ int sched_cpu_deactivate(unsigned int cpu)
 	 */
 	sched_smt_present_dec(cpu);
 
-#ifdef CONFIG_SCHED_SMT
 	sched_core_cpu_deactivate(cpu);
-#endif
 
 	if (!sched_smp_initialized)
 		return 0;
diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index 7468560a6d80..2bcf58e99c9b 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -79,7 +79,6 @@ static bool scx_idle_test_and_clear_cpu(int cpu)
 	int node = scx_cpu_node_if_enabled(cpu);
 	struct cpumask *idle_cpus = idle_cpumask(node)->cpu;
 
-#ifdef CONFIG_SCHED_SMT
 	/*
 	 * SMT mask should be cleared whether we can claim @cpu or not. The SMT
 	 * cluster is not wholly idle either way. This also prevents
@@ -104,7 +103,6 @@ static bool scx_idle_test_and_clear_cpu(int cpu)
 		else if (cpumask_test_cpu(cpu, idle_smts))
 			__cpumask_clear_cpu(cpu, idle_smts);
 	}
-#endif
 
 	return cpumask_test_and_clear_cpu(cpu, idle_cpus);
 }
@@ -622,7 +620,6 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
 		goto out_unlock;
 	}
 
-#ifdef CONFIG_SCHED_SMT
 	/*
 	 * Use @prev_cpu's sibling if it's idle.
 	 */
@@ -634,7 +631,6 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
 				goto out_unlock;
 		}
 	}
-#endif
 
 	/*
 	 * Search for any idle CPU in the same LLC domain.
@@ -714,7 +710,6 @@ static void update_builtin_idle(int cpu, bool idle)
 
 	assign_cpu(cpu, idle_cpus, idle);
 
-#ifdef CONFIG_SCHED_SMT
 	if (sched_smt_active()) {
 		const struct cpumask *smt = cpu_smt_mask(cpu);
 		struct cpumask *idle_smts = idle_cpumask(node)->smt;
@@ -731,7 +726,6 @@ static void update_builtin_idle(int cpu, bool idle)
 			cpumask_andnot(idle_smts, idle_smts, smt);
 		}
 	}
-#endif
 }
 
 /*
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 09d3acd2d2bc..233bd2ebbb73 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1555,7 +1555,6 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
 
 static inline bool is_core_idle(int cpu)
 {
-#ifdef CONFIG_SCHED_SMT
 	int sibling;
 
 	for_each_cpu(sibling, cpu_smt_mask(cpu)) {
@@ -1565,7 +1564,6 @@ static inline bool is_core_idle(int cpu)
 		if (!idle_cpu(sibling))
 			return false;
 	}
-#endif
 
 	return true;
 }
@@ -2248,7 +2246,6 @@ 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);
 static inline int numa_idle_core(int idle_core, int cpu)
@@ -2266,12 +2263,6 @@ static inline int numa_idle_core(int idle_core, int cpu)
 
 	return idle_core;
 }
-#else /* !CONFIG_SCHED_SMT: */
-static inline int numa_idle_core(int idle_core, int cpu)
-{
-	return idle_core;
-}
-#endif /* !CONFIG_SCHED_SMT */
 
 /*
  * Gather all necessary information to make NUMA balancing placement
@@ -7778,7 +7769,6 @@ static inline int __select_idle_cpu(int cpu, struct task_struct *p)
 	return -1;
 }
 
-#ifdef CONFIG_SCHED_SMT
 DEFINE_STATIC_KEY_FALSE(sched_smt_present);
 EXPORT_SYMBOL_GPL(sched_smt_present);
 
@@ -7888,29 +7878,6 @@ static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int t
 	return -1;
 }
 
-#else /* !CONFIG_SCHED_SMT: */
-
-static inline void set_idle_cores(int cpu, int val)
-{
-}
-
-static inline bool test_idle_cores(int cpu)
-{
-	return false;
-}
-
-static inline int select_idle_core(struct task_struct *p, int core, struct cpumask *cpus, int *idle_cpu)
-{
-	return __select_idle_cpu(core, p);
-}
-
-static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
-{
-	return -1;
-}
-
-#endif /* !CONFIG_SCHED_SMT */
-
 /*
  * Scan the LLC domain for idle CPUs; this is dynamically regulated by
  * comparing the average scan cost (tracked in sd->avg_scan_cost) against the
@@ -12002,9 +11969,7 @@ static int should_we_balance(struct lb_env *env)
 			 * idle has been found, then its not needed to check other
 			 * SMT siblings for idleness:
 			 */
-#ifdef CONFIG_SCHED_SMT
 			cpumask_andnot(swb_cpus, swb_cpus, cpu_smt_mask(cpu));
-#endif
 			continue;
 		}
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9f63b15d309d..e476623a0c2a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1667,7 +1667,6 @@ do {						\
 	flags = _raw_spin_rq_lock_irqsave(rq);	\
 } while (0)
 
-#ifdef CONFIG_SCHED_SMT
 extern void __update_idle_core(struct rq *rq);
 
 static inline void update_idle_core(struct rq *rq)
@@ -1676,12 +1675,7 @@ static inline void update_idle_core(struct rq *rq)
 		__update_idle_core(rq);
 }
 
-#else /* !CONFIG_SCHED_SMT: */
-static inline void update_idle_core(struct rq *rq) { }
-#endif /* !CONFIG_SCHED_SMT */
-
 #ifdef CONFIG_FAIR_GROUP_SCHED
-
 static inline struct task_struct *task_of(struct sched_entity *se)
 {
 	WARN_ON_ONCE(!entity_is_task(se));
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 5847b83d9d55..a1f46e3f4ede 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1310,9 +1310,7 @@ static void init_sched_groups_capacity(int cpu, struct sched_domain *sd)
 		cpumask_copy(mask, sched_group_span(sg));
 		for_each_cpu(cpu, mask) {
 			cores++;
-#ifdef CONFIG_SCHED_SMT
 			cpumask_andnot(mask, mask, cpu_smt_mask(cpu));
-#endif
 		}
 		sg->cores = cores;