Messages in this thread Patch in this message | | | Date | Thu, 22 Apr 2021 14:05:04 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 05/19] sched: Core-wide rq->lock |
| |
Introduce the basic infrastructure to have a core wide rq->lock.
This relies on the rq->__lock order being in increasing CPU number. It is also constrained to SMT8 per lockdep (and SMT256 per preempt_count).
Luckily SMT8 is the max supported SMT count for Linux (Mips, Sparc and Power are known to have this).
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/Kconfig.preempt | 6 ++ kernel/sched/core.c | 139 +++++++++++++++++++++++++++++++++++++++++++++++++ kernel/sched/sched.h | 37 +++++++++++++ 3 files changed, 182 insertions(+)
--- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -99,3 +99,9 @@ config PREEMPT_DYNAMIC Interesting if you want the same pre-built kernel should be used for both Server and Desktop workloads. + +config SCHED_CORE + bool "Core Scheduling for SMT" + default y + depends on SCHED_SMT + --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -84,6 +84,103 @@ unsigned int sysctl_sched_rt_period = 10 __read_mostly int scheduler_running; +#ifdef CONFIG_SCHED_CORE + +DEFINE_STATIC_KEY_FALSE(__sched_core_enabled); + +/* + * Magic required such that: + * + * raw_spin_rq_lock(rq); + * ... + * raw_spin_rq_unlock(rq); + * + * ends up locking and unlocking the _same_ lock, and all CPUs + * always agree on what rq has what lock. + * + * XXX entirely possible to selectively enable cores, don't bother for now. + */ + +static DEFINE_MUTEX(sched_core_mutex); +static int sched_core_count; +static struct cpumask sched_core_mask; + +static void __sched_core_flip(bool enabled) +{ + int cpu, t, i; + + cpus_read_lock(); + + /* + * Toggle the online cores, one by one. + */ + cpumask_copy(&sched_core_mask, cpu_online_mask); + for_each_cpu(cpu, &sched_core_mask) { + const struct cpumask *smt_mask = cpu_smt_mask(cpu); + + i = 0; + local_irq_disable(); + for_each_cpu(t, smt_mask) { + /* supports up to SMT8 */ + raw_spin_lock_nested(&cpu_rq(t)->__lock, i++); + } + + for_each_cpu(t, smt_mask) + cpu_rq(t)->core_enabled = enabled; + + for_each_cpu(t, smt_mask) + raw_spin_unlock(&cpu_rq(t)->__lock); + local_irq_enable(); + + cpumask_andnot(&sched_core_mask, &sched_core_mask, smt_mask); + } + + /* + * Toggle the offline CPUs. + */ + cpumask_copy(&sched_core_mask, cpu_possible_mask); + cpumask_andnot(&sched_core_mask, &sched_core_mask, cpu_online_mask); + + for_each_cpu(cpu, &sched_core_mask) + cpu_rq(cpu)->core_enabled = enabled; + + cpus_read_unlock(); +} + +static void __sched_core_enable(void) +{ + // XXX verify there are no cookie tasks (yet) + + static_branch_enable(&__sched_core_enabled); + __sched_core_flip(true); +} + +static void __sched_core_disable(void) +{ + // XXX verify there are no cookie tasks (left) + + __sched_core_flip(false); + static_branch_disable(&__sched_core_enabled); +} + +void sched_core_get(void) +{ + mutex_lock(&sched_core_mutex); + if (!sched_core_count++) + __sched_core_enable(); + mutex_unlock(&sched_core_mutex); +} + +void sched_core_put(void) +{ + mutex_lock(&sched_core_mutex); + if (!--sched_core_count) + __sched_core_disable(); + mutex_unlock(&sched_core_mutex); +} + +#endif /* CONFIG_SCHED_CORE */ + /* * part of the period that we allow rt tasks to run in us. * default: 0.95s @@ -5042,6 +5139,40 @@ pick_next_task(struct rq *rq, struct tas BUG(); } +#ifdef CONFIG_SCHED_CORE + +static inline void sched_core_cpu_starting(unsigned int cpu) +{ + const struct cpumask *smt_mask = cpu_smt_mask(cpu); + struct rq *rq, *core_rq = NULL; + int i; + + core_rq = cpu_rq(cpu)->core; + + if (!core_rq) { + for_each_cpu(i, smt_mask) { + rq = cpu_rq(i); + if (rq->core && rq->core == rq) + core_rq = rq; + } + + if (!core_rq) + core_rq = cpu_rq(cpu); + + for_each_cpu(i, smt_mask) { + rq = cpu_rq(i); + + WARN_ON_ONCE(rq->core && rq->core != core_rq); + rq->core = core_rq; + } + } +} +#else /* !CONFIG_SCHED_CORE */ + +static inline void sched_core_cpu_starting(unsigned int cpu) {} + +#endif /* CONFIG_SCHED_CORE */ + /* * __schedule() is the main scheduler function. * @@ -8006,6 +8137,7 @@ static void sched_rq_cpu_starting(unsign int sched_cpu_starting(unsigned int cpu) { + sched_core_cpu_starting(cpu); sched_rq_cpu_starting(cpu); sched_tick_start(cpu); return 0; @@ -8290,6 +8424,11 @@ void __init sched_init(void) #endif /* CONFIG_SMP */ hrtick_rq_init(rq); atomic_set(&rq->nr_iowait, 0); + +#ifdef CONFIG_SCHED_CORE + rq->core = NULL; + rq->core_enabled = 0; +#endif } set_load_weight(&init_task, false); --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1075,6 +1075,12 @@ struct rq { #endif unsigned int push_busy; struct cpu_stop_work push_work; + +#ifdef CONFIG_SCHED_CORE + /* per rq */ + struct rq *core; + unsigned int core_enabled; +#endif }; #ifdef CONFIG_FAIR_GROUP_SCHED @@ -1113,6 +1119,35 @@ static inline bool is_migration_disabled #endif } +#ifdef CONFIG_SCHED_CORE + +DECLARE_STATIC_KEY_FALSE(__sched_core_enabled); + +static inline bool sched_core_enabled(struct rq *rq) +{ + return static_branch_unlikely(&__sched_core_enabled) && rq->core_enabled; +} + +static inline bool sched_core_disabled(void) +{ + return !static_branch_unlikely(&__sched_core_enabled); +} + +static inline raw_spinlock_t *rq_lockp(struct rq *rq) +{ + if (sched_core_enabled(rq)) + return &rq->core->__lock; + + return &rq->__lock; +} + +#else /* !CONFIG_SCHED_CORE */ + +static inline bool sched_core_enabled(struct rq *rq) +{ + return false; +} + static inline bool sched_core_disabled(void) { return true; @@ -1123,6 +1158,8 @@ static inline raw_spinlock_t *rq_lockp(s return &rq->__lock; } +#endif /* CONFIG_SCHED_CORE */ + static inline void lockdep_assert_rq_held(struct rq *rq) { lockdep_assert_held(rq_lockp(rq));
| |