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

diff --git a/include/linux/sched/smt.h b/include/linux/sched/smt.h
index 166b19af956f8b922007428b06b10f4e0d023542..cde6679c02781d6689c9eae123260e51a426a9a5 100644 (file)
--- a/include/linux/sched/smt.h
+++ b/include/linux/sched/smt.h
@@ -4,16 +4,12 @@
 
 #include <linux/static_key.h>
 
-#ifdef CONFIG_SCHED_SMT
 extern struct static_key_false sched_smt_present;
 
 static __always_inline bool sched_smt_active(void)
 {
        return static_branch_likely(&sched_smt_present);
 }
-#else
-static __always_inline bool sched_smt_active(void) { return false; }
-#endif
 
 void arch_smt_update(void);
 

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b905805bbcbe4ace262dc482fe774c047d350124..3ae5f19c1b7eb197f69baffc474e87e139ea0a46 100644 (file)
--- 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 7468560a6d80414504b6e1266814c2216706d0cd..2bcf58e99c9b5b7347cd860994ef961e715a2ec3 100644 (file)
--- 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 09d3acd2d2bcf9b6845ea2d974f9995118151cd3..233bd2ebbb738d1e301e7eb98b089e6e2b38bb2a 100644 (file)
--- 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 9f63b15d309d11f416783c54da04e61d09512311..e476623a0c2af7ed67123511eafdbfb85ae7913f 100644 (file)
--- 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 5847b83d9d552bd13c13c48f710c32cf9f85a2ff..a1f46e3f4edea3686c64157fe32a7511c93cf9ec 100644 (file)
--- 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;
 

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 3fe6b0c99f3d89a4adb3cc3bf18c5b22fa096a3c..773d8e9ae30c542677de49a00bb6c4e2cfe660b1 100644 (file)
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -633,6 +633,11 @@ int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
 EXPORT_SYMBOL_GPL(stop_machine);
 
 #ifdef CONFIG_SCHED_SMT
+/*
+ * INTEL_IFS is the only user of this API. That selftest can
+ * only be compiled if SMP=y. On x86 it selects SCHED_SMT.
+ * Keep the ifdefs for now.
+ */
 int stop_core_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data)
 {
        const struct cpumask *smt_mask = cpu_smt_mask(cpu);

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 5f747f241a5f1e151c071b7357d033492250bbdc..99ef412f02a6873df24a5373fcfc4665922b30f8 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -8187,11 +8187,7 @@ static bool __init cpus_dont_share(int cpu0, int cpu1)
 
 static bool __init cpus_share_smt(int cpu0, int cpu1)
 {
-#ifdef CONFIG_SCHED_SMT
        return cpumask_test_cpu(cpu0, cpu_smt_mask(cpu1));
-#else
-       return false;
-#endif
 }
 
 static bool __init cpus_share_numa(int cpu0, int cpu1)