From: Shrikanth Hegde Date: Fri, 15 May 2026 17:24:54 +0000 (+0530) Subject: sched: Simplify ifdeffery around cpu_smt_mask X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5bc6ab2d42e545f816def21cfcdb4ba35cc74bf6;p=thirdparty%2Fkernel%2Flinux.git 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 Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Phil Auld Reviewed-by: Valentin Schneider Acked-by: Tejun Heo Tested-by: K Prateek Nayak 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 166b19af956f8..cde6679c02781 100644 --- a/include/linux/sched/smt.h +++ b/include/linux/sched/smt.h @@ -4,16 +4,12 @@ #include -#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 b905805bbcbe4..3ae5f19c1b7eb 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 7468560a6d804..2bcf58e99c9b5 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 09d3acd2d2bcf..233bd2ebbb738 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 9f63b15d309d1..e476623a0c2af 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 5847b83d9d552..a1f46e3f4edea 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; diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 3fe6b0c99f3d8..773d8e9ae30c5 100644 --- 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 5f747f241a5f1..99ef412f02a68 100644 --- 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)