From 5ddf15cb65a8c14868cdc743474bd0a4fa9b586f Mon Sep 17 00:00:00 2001 From: Eric Naim Date: Fri, 13 Dec 2024 23:03:09 +0800 Subject: [PATCH] preempt-lazy Signed-off-by: Eric Naim --- arch/x86/Kconfig | 1 + arch/x86/include/asm/thread_info.h | 6 +- include/linux/entry-common.h | 3 +- include/linux/entry-kvm.h | 5 +- include/linux/preempt.h | 8 +- include/linux/rcupdate.h | 2 +- include/linux/rcutree.h | 2 +- include/linux/sched.h | 3 +- include/linux/srcutiny.h | 2 +- include/linux/thread_info.h | 21 +++++- include/linux/trace_events.h | 8 +- kernel/Kconfig.preempt | 25 ++++++- kernel/entry/common.c | 2 +- kernel/entry/kvm.c | 4 +- kernel/rcu/Kconfig | 4 +- kernel/rcu/srcutiny.c | 14 ++-- kernel/rcu/tree_plugin.h | 22 ++++-- kernel/sched/core.c | 116 +++++++++++++++++++++++++---- kernel/sched/debug.c | 7 +- kernel/sched/fair.c | 6 +- kernel/sched/sched.h | 1 + kernel/trace/trace.c | 2 + kernel/trace/trace_osnoise.c | 32 ++++---- kernel/trace/trace_output.c | 16 +++- 24 files changed, 232 insertions(+), 80 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index f127d0f1024e..4b28c191ae31 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -93,6 +93,7 @@ config X86 select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE select ARCH_HAS_PMEM_API if X86_64 + select ARCH_HAS_PREEMPT_LAZY select ARCH_HAS_PTE_DEVMAP if X86_64 select ARCH_HAS_PTE_SPECIAL select ARCH_HAS_HW_PTE_YOUNG diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h index 12da7dfd5ef1..a55c214f3ba6 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -87,8 +87,9 @@ struct thread_info { #define TIF_NOTIFY_RESUME 1 /* callback before returning to user */ #define TIF_SIGPENDING 2 /* signal pending */ #define TIF_NEED_RESCHED 3 /* rescheduling necessary */ -#define TIF_SINGLESTEP 4 /* reenable singlestep on user return*/ -#define TIF_SSBD 5 /* Speculative store bypass disable */ +#define TIF_NEED_RESCHED_LAZY 4 /* Lazy rescheduling needed */ +#define TIF_SINGLESTEP 5 /* reenable singlestep on user return*/ +#define TIF_SSBD 6 /* Speculative store bypass disable */ #define TIF_SPEC_IB 9 /* Indirect branch speculation mitigation */ #define TIF_SPEC_L1D_FLUSH 10 /* Flush L1D on mm switches (processes) */ #define TIF_USER_RETURN_NOTIFY 11 /* notify kernel of userspace return */ @@ -110,6 +111,7 @@ struct thread_info { #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME) #define _TIF_SIGPENDING (1 << TIF_SIGPENDING) #define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED) +#define _TIF_NEED_RESCHED_LAZY (1 << TIF_NEED_RESCHED_LAZY) #define _TIF_SINGLESTEP (1 << TIF_SINGLESTEP) #define _TIF_SSBD (1 << TIF_SSBD) #define _TIF_SPEC_IB (1 << TIF_SPEC_IB) diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h index 1e50cdb83ae5..fc61d0205c97 100644 --- a/include/linux/entry-common.h +++ b/include/linux/entry-common.h @@ -64,7 +64,8 @@ #define EXIT_TO_USER_MODE_WORK \ (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ - _TIF_NEED_RESCHED | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \ + _TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY | \ + _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \ ARCH_EXIT_TO_USER_MODE_WORK) /** diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h index 6813171afccb..16149f6625e4 100644 --- a/include/linux/entry-kvm.h +++ b/include/linux/entry-kvm.h @@ -17,8 +17,9 @@ #endif #define XFER_TO_GUEST_MODE_WORK \ - (_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL | \ - _TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK) + (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY | _TIF_SIGPENDING | \ + _TIF_NOTIFY_SIGNAL | _TIF_NOTIFY_RESUME | \ + ARCH_XFER_TO_GUEST_MODE_WORK) struct kvm_vcpu; diff --git a/include/linux/preempt.h b/include/linux/preempt.h index ce76f1a45722..ca86235ac15c 100644 --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -486,6 +486,7 @@ DEFINE_LOCK_GUARD_0(migrate, migrate_disable(), migrate_enable()) extern bool preempt_model_none(void); extern bool preempt_model_voluntary(void); extern bool preempt_model_full(void); +extern bool preempt_model_lazy(void); #else @@ -502,6 +503,11 @@ static inline bool preempt_model_full(void) return IS_ENABLED(CONFIG_PREEMPT); } +static inline bool preempt_model_lazy(void) +{ + return IS_ENABLED(CONFIG_PREEMPT_LAZY); +} + #endif static inline bool preempt_model_rt(void) @@ -519,7 +525,7 @@ static inline bool preempt_model_rt(void) */ static inline bool preempt_model_preemptible(void) { - return preempt_model_full() || preempt_model_rt(); + return preempt_model_full() || preempt_model_lazy() || preempt_model_rt(); } #endif /* __LINUX_PREEMPT_H */ diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 48e5c03df1dd..257e9ae34414 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -95,9 +95,9 @@ static inline void __rcu_read_lock(void) static inline void __rcu_read_unlock(void) { - preempt_enable(); if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) rcu_read_unlock_strict(); + preempt_enable(); } static inline int rcu_preempt_depth(void) diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 90a684f94776..ae8b5cb475a3 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -104,7 +104,7 @@ extern int rcu_scheduler_active; void rcu_end_inkernel_boot(void); bool rcu_inkernel_boot_has_ended(void); bool rcu_is_watching(void); -#ifndef CONFIG_PREEMPTION +#ifndef CONFIG_PREEMPT_RCU void rcu_all_qs(void); #endif diff --git a/include/linux/sched.h b/include/linux/sched.h index bb343136ddd0..ade641760900 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2002,7 +2002,8 @@ static inline void set_tsk_need_resched(struct task_struct *tsk) static inline void clear_tsk_need_resched(struct task_struct *tsk) { - clear_tsk_thread_flag(tsk,TIF_NEED_RESCHED); + atomic_long_andnot(_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY, + (atomic_long_t *)&task_thread_info(tsk)->flags); } static inline int test_tsk_need_resched(struct task_struct *tsk) diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h index 4d96bbdb45f0..1635c5e2662f 100644 --- a/include/linux/srcutiny.h +++ b/include/linux/srcutiny.h @@ -64,7 +64,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp) { int idx; - preempt_disable(); // Needed for PREEMPT_AUTO + preempt_disable(); // Needed for PREEMPT_LAZY idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1; WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1); preempt_enable(); diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h index 9ea0b28068f4..cf2446c9c30d 100644 --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -59,6 +59,14 @@ enum syscall_work_bit { #include +#ifndef TIF_NEED_RESCHED_LAZY +#ifdef CONFIG_ARCH_HAS_PREEMPT_LAZY +#error Inconsistent PREEMPT_LAZY +#endif +#define TIF_NEED_RESCHED_LAZY TIF_NEED_RESCHED +#define _TIF_NEED_RESCHED_LAZY _TIF_NEED_RESCHED +#endif + #ifdef __KERNEL__ #ifndef arch_set_restart_data @@ -179,22 +187,27 @@ static __always_inline unsigned long read_ti_thread_flags(struct thread_info *ti #ifdef _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H -static __always_inline bool tif_need_resched(void) +static __always_inline bool tif_test_bit(int bit) { - return arch_test_bit(TIF_NEED_RESCHED, + return arch_test_bit(bit, (unsigned long *)(¤t_thread_info()->flags)); } #else -static __always_inline bool tif_need_resched(void) +static __always_inline bool tif_test_bit(int bit) { - return test_bit(TIF_NEED_RESCHED, + return test_bit(bit, (unsigned long *)(¤t_thread_info()->flags)); } #endif /* _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H */ +static __always_inline bool tif_need_resched(void) +{ + return tif_test_bit(TIF_NEED_RESCHED); +} + #ifndef CONFIG_HAVE_ARCH_WITHIN_STACK_FRAMES static inline int arch_within_stack_frames(const void * const stack, const void * const stackend, diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h index 42bedcddd511..4cae6f258137 100644 --- a/include/linux/trace_events.h +++ b/include/linux/trace_events.h @@ -184,8 +184,8 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status); enum trace_flag_type { TRACE_FLAG_IRQS_OFF = 0x01, - TRACE_FLAG_IRQS_NOSUPPORT = 0x02, - TRACE_FLAG_NEED_RESCHED = 0x04, + TRACE_FLAG_NEED_RESCHED = 0x02, + TRACE_FLAG_NEED_RESCHED_LAZY = 0x04, TRACE_FLAG_HARDIRQ = 0x08, TRACE_FLAG_SOFTIRQ = 0x10, TRACE_FLAG_PREEMPT_RESCHED = 0x20, @@ -211,11 +211,11 @@ static inline unsigned int tracing_gen_ctx(void) static inline unsigned int tracing_gen_ctx_flags(unsigned long irqflags) { - return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT); + return tracing_gen_ctx_irq_test(0); } static inline unsigned int tracing_gen_ctx(void) { - return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT); + return tracing_gen_ctx_irq_test(0); } #endif diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt index fe782cd77388..7c1b29a3a491 100644 --- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -11,12 +11,16 @@ config PREEMPT_BUILD select PREEMPTION select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK +config ARCH_HAS_PREEMPT_LAZY + bool + choice prompt "Preemption Model" default PREEMPT_NONE config PREEMPT_NONE bool "No Forced Preemption (Server)" + depends on !PREEMPT_RT select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC help This is the traditional Linux preemption model, geared towards @@ -32,6 +36,7 @@ config PREEMPT_NONE config PREEMPT_VOLUNTARY bool "Voluntary Kernel Preemption (Desktop)" depends on !ARCH_NO_PREEMPT + depends on !PREEMPT_RT select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC help This option reduces the latency of the kernel by adding more @@ -51,7 +56,7 @@ config PREEMPT_VOLUNTARY config PREEMPT bool "Preemptible Kernel (Low-Latency Desktop)" depends on !ARCH_NO_PREEMPT - select PREEMPT_BUILD + select PREEMPT_BUILD if !PREEMPT_DYNAMIC help This option reduces the latency of the kernel by making all kernel code (that is not executing in a critical section) @@ -67,6 +72,20 @@ config PREEMPT embedded system with latency requirements in the milliseconds range. +config PREEMPT_LAZY + bool "Scheduler controlled preemption model" + depends on !ARCH_NO_PREEMPT + depends on ARCH_HAS_PREEMPT_LAZY + select PREEMPT_BUILD if !PREEMPT_DYNAMIC + help + This option provides a scheduler driven preemption model that + is fundamentally similar to full preemption, but is less + eager to preempt SCHED_NORMAL tasks in an attempt to + reduce lock holder preemption and recover some of the performance + gains seen from using Voluntary preemption. + +endchoice + config PREEMPT_RT bool "Fully Preemptible Kernel (Real-Time)" depends on EXPERT && ARCH_SUPPORTS_RT @@ -84,8 +103,6 @@ config PREEMPT_RT Select this if you are building a kernel for systems which require real-time guarantees. -endchoice - config PREEMPT_COUNT bool @@ -95,7 +112,7 @@ config PREEMPTION config PREEMPT_DYNAMIC bool "Preemption behaviour defined on boot" - depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT + depends on HAVE_PREEMPT_DYNAMIC select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY select PREEMPT_BUILD default y if HAVE_PREEMPT_DYNAMIC_CALL diff --git a/kernel/entry/common.c b/kernel/entry/common.c index 5b6934e23c21..e33691d5adf7 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -98,7 +98,7 @@ __always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs, local_irq_enable_exit_to_user(ti_work); - if (ti_work & _TIF_NEED_RESCHED) + if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) schedule(); if (ti_work & _TIF_UPROBE) diff --git a/kernel/entry/kvm.c b/kernel/entry/kvm.c index 2e0f75bcb7fd..8485f63863af 100644 --- a/kernel/entry/kvm.c +++ b/kernel/entry/kvm.c @@ -13,7 +13,7 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work) return -EINTR; } - if (ti_work & _TIF_NEED_RESCHED) + if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) schedule(); if (ti_work & _TIF_NOTIFY_RESUME) @@ -24,7 +24,7 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work) return ret; ti_work = read_thread_flags(); - } while (ti_work & XFER_TO_GUEST_MODE_WORK || need_resched()); + } while (ti_work & XFER_TO_GUEST_MODE_WORK); return 0; } diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index 3e079de0f5b4..9d52f87fac27 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -18,7 +18,7 @@ config TREE_RCU config PREEMPT_RCU bool - default y if PREEMPTION + default y if (PREEMPT || PREEMPT_RT || PREEMPT_DYNAMIC) select TREE_RCU help This option selects the RCU implementation that is @@ -91,7 +91,7 @@ config NEED_TASKS_RCU config TASKS_RCU bool - default NEED_TASKS_RCU && (PREEMPTION || PREEMPT_AUTO) + default NEED_TASKS_RCU && PREEMPTION select IRQ_WORK config FORCE_TASKS_RUDE_RCU diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c index 4dcbf8aa80ff..f688bdad293e 100644 --- a/kernel/rcu/srcutiny.c +++ b/kernel/rcu/srcutiny.c @@ -98,7 +98,7 @@ void __srcu_read_unlock(struct srcu_struct *ssp, int idx) { int newval; - preempt_disable(); // Needed for PREEMPT_AUTO + preempt_disable(); // Needed for PREEMPT_LAZY newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1; WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval); preempt_enable(); @@ -120,7 +120,7 @@ void srcu_drive_gp(struct work_struct *wp) struct srcu_struct *ssp; ssp = container_of(wp, struct srcu_struct, srcu_work); - preempt_disable(); // Needed for PREEMPT_AUTO + preempt_disable(); // Needed for PREEMPT_LAZY if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) { preempt_enable(); return; /* Already running or nothing to do. */ @@ -138,7 +138,7 @@ void srcu_drive_gp(struct work_struct *wp) WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ preempt_enable(); swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx])); - preempt_disable(); // Needed for PREEMPT_AUTO + preempt_disable(); // Needed for PREEMPT_LAZY WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); preempt_enable(); @@ -159,7 +159,7 @@ void srcu_drive_gp(struct work_struct *wp) * at interrupt level, but the ->srcu_gp_running checks will * straighten that out. */ - preempt_disable(); // Needed for PREEMPT_AUTO + preempt_disable(); // Needed for PREEMPT_LAZY WRITE_ONCE(ssp->srcu_gp_running, false); idx = ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)); preempt_enable(); @@ -172,7 +172,7 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp) { unsigned long cookie; - preempt_disable(); // Needed for PREEMPT_AUTO + preempt_disable(); // Needed for PREEMPT_LAZY cookie = get_state_synchronize_srcu(ssp); if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) { preempt_enable(); @@ -199,7 +199,7 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, rhp->func = func; rhp->next = NULL; - preempt_disable(); // Needed for PREEMPT_AUTO + preempt_disable(); // Needed for PREEMPT_LAZY local_irq_save(flags); *ssp->srcu_cb_tail = rhp; ssp->srcu_cb_tail = &rhp->next; @@ -261,7 +261,7 @@ unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) { unsigned long ret; - preempt_disable(); // Needed for PREEMPT_AUTO + preempt_disable(); // Needed for PREEMPT_LAZY ret = get_state_synchronize_srcu(ssp); srcu_gp_start_if_needed(ssp); preempt_enable(); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 1c7cbd145d5e..304e3405e6ec 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -832,8 +832,17 @@ void rcu_read_unlock_strict(void) { struct rcu_data *rdp; - if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread) + if (irqs_disabled() || in_atomic_preempt_off() || !rcu_state.gp_kthread) return; + + /* + * rcu_report_qs_rdp() can only be invoked with a stable rdp and + * from the local CPU. + * + * The in_atomic_preempt_off() check ensures that we come here holding + * the last preempt_count (which will get dropped once we return to + * __rcu_read_unlock(). + */ rdp = this_cpu_ptr(&rcu_data); rdp->cpu_no_qs.b.norm = false; rcu_report_qs_rdp(rdp); @@ -974,13 +983,16 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) */ static void rcu_flavor_sched_clock_irq(int user) { - if (user || rcu_is_cpu_rrupt_from_idle()) { + if (user || rcu_is_cpu_rrupt_from_idle() || + (IS_ENABLED(CONFIG_PREEMPT_COUNT) && + (preempt_count() == HARDIRQ_OFFSET))) { /* * Get here if this CPU took its interrupt from user - * mode or from the idle loop, and if this is not a - * nested interrupt. In this case, the CPU is in - * a quiescent state, so note it. + * mode, from the idle loop without this being a nested + * interrupt, or while not holding the task preempt count + * (with PREEMPT_COUNT=y). In this case, the CPU is in a + * quiescent state, so note it. * * No memory barrier is required here because rcu_qs() * references only CPU-local variables that other CPUs diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 76b27b2a9c56..e82948e247c1 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -941,10 +941,9 @@ static inline void hrtick_rq_init(struct rq *rq) * this avoids any races wrt polling state changes and thereby avoids * spurious IPIs. */ -static inline bool set_nr_and_not_polling(struct task_struct *p) +static inline bool set_nr_and_not_polling(struct thread_info *ti, int tif) { - struct thread_info *ti = task_thread_info(p); - return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG); + return !(fetch_or(&ti->flags, 1 << tif) & _TIF_POLLING_NRFLAG); } /* @@ -969,9 +968,9 @@ static bool set_nr_if_polling(struct task_struct *p) } #else -static inline bool set_nr_and_not_polling(struct task_struct *p) +static inline bool set_nr_and_not_polling(struct thread_info *ti, int tif) { - set_tsk_need_resched(p); + atomic_long_or(1 << tif, (atomic_long_t *)&ti->flags); return true; } @@ -1076,28 +1075,66 @@ void wake_up_q(struct wake_q_head *head) * might also involve a cross-CPU call to trigger the scheduler on * the target CPU. */ -void resched_curr(struct rq *rq) +static void __resched_curr(struct rq *rq, int tif) { struct task_struct *curr = rq->curr; + struct thread_info *cti = task_thread_info(curr); int cpu; lockdep_assert_rq_held(rq); - if (test_tsk_need_resched(curr)) + if (is_idle_task(curr) && tif == TIF_NEED_RESCHED_LAZY) + tif = TIF_NEED_RESCHED; + + if (cti->flags & ((1 << tif) | _TIF_NEED_RESCHED)) return; cpu = cpu_of(rq); if (cpu == smp_processor_id()) { - set_tsk_need_resched(curr); - set_preempt_need_resched(); + set_ti_thread_flag(cti, tif); + if (tif == TIF_NEED_RESCHED) + set_preempt_need_resched(); return; } - if (set_nr_and_not_polling(curr)) - smp_send_reschedule(cpu); - else + if (set_nr_and_not_polling(cti, tif)) { + if (tif == TIF_NEED_RESCHED) + smp_send_reschedule(cpu); + } else { trace_sched_wake_idle_without_ipi(cpu); + } +} + +void resched_curr(struct rq *rq) +{ + __resched_curr(rq, TIF_NEED_RESCHED); +} + +#ifdef CONFIG_PREEMPT_DYNAMIC +static DEFINE_STATIC_KEY_FALSE(sk_dynamic_preempt_lazy); +static __always_inline bool dynamic_preempt_lazy(void) +{ + return static_branch_unlikely(&sk_dynamic_preempt_lazy); +} +#else +static __always_inline bool dynamic_preempt_lazy(void) +{ + return IS_ENABLED(CONFIG_PREEMPT_LAZY); +} +#endif + +static __always_inline int tif_need_resched_lazy(void) +{ + if (dynamic_preempt_lazy()) + return TIF_NEED_RESCHED_LAZY; + + return TIF_NEED_RESCHED; +} + +void resched_curr_lazy(struct rq *rq) +{ + __resched_curr(rq, tif_need_resched_lazy()); } void resched_cpu(int cpu) @@ -1192,7 +1229,7 @@ static void wake_up_idle_cpu(int cpu) * and testing of the above solutions didn't appear to report * much benefits. */ - if (set_nr_and_not_polling(rq->idle)) + if (set_nr_and_not_polling(task_thread_info(rq->idle), TIF_NEED_RESCHED)) smp_send_reschedule(cpu); else trace_sched_wake_idle_without_ipi(cpu); @@ -5604,6 +5641,10 @@ void sched_tick(void) update_rq_clock(rq); hw_pressure = arch_scale_hw_pressure(cpu_of(rq)); update_hw_load_avg(rq_clock_task(rq), rq, hw_pressure); + + if (dynamic_preempt_lazy() && tif_test_bit(TIF_NEED_RESCHED_LAZY)) + resched_curr(rq); + curr->sched_class->task_tick(rq, curr, 0); if (sched_feat(LATENCY_WARN)) resched_latency = cpu_resched_latency(rq); @@ -7219,7 +7260,7 @@ int __sched __cond_resched(void) return 1; } /* - * In preemptible kernels, ->rcu_read_lock_nesting tells the tick + * In PREEMPT_RCU kernels, ->rcu_read_lock_nesting tells the tick * whether the current CPU is in an RCU read-side critical section, * so the tick can report quiescent states even for CPUs looping * in kernel context. In contrast, in non-preemptible kernels, @@ -7228,6 +7269,8 @@ int __sched __cond_resched(void) * RCU quiescent state. Therefore, the following code causes * cond_resched() to report a quiescent state, but only when RCU * is in urgent need of one. + * A third case, preemptible, but non-PREEMPT_RCU provides for + * urgently needed quiescent states via rcu_flavor_sched_clock_irq(). */ #ifndef CONFIG_PREEMPT_RCU rcu_all_qs(); @@ -7352,6 +7395,7 @@ EXPORT_SYMBOL(__cond_resched_rwlock_write); * preempt_schedule <- NOP * preempt_schedule_notrace <- NOP * irqentry_exit_cond_resched <- NOP + * dynamic_preempt_lazy <- false * * VOLUNTARY: * cond_resched <- __cond_resched @@ -7359,6 +7403,7 @@ EXPORT_SYMBOL(__cond_resched_rwlock_write); * preempt_schedule <- NOP * preempt_schedule_notrace <- NOP * irqentry_exit_cond_resched <- NOP + * dynamic_preempt_lazy <- false * * FULL: * cond_resched <- RET0 @@ -7366,6 +7411,15 @@ EXPORT_SYMBOL(__cond_resched_rwlock_write); * preempt_schedule <- preempt_schedule * preempt_schedule_notrace <- preempt_schedule_notrace * irqentry_exit_cond_resched <- irqentry_exit_cond_resched + * dynamic_preempt_lazy <- false + * + * LAZY: + * cond_resched <- RET0 + * might_resched <- RET0 + * preempt_schedule <- preempt_schedule + * preempt_schedule_notrace <- preempt_schedule_notrace + * irqentry_exit_cond_resched <- irqentry_exit_cond_resched + * dynamic_preempt_lazy <- true */ enum { @@ -7373,30 +7427,41 @@ enum { preempt_dynamic_none, preempt_dynamic_voluntary, preempt_dynamic_full, + preempt_dynamic_lazy, }; int preempt_dynamic_mode = preempt_dynamic_undefined; int sched_dynamic_mode(const char *str) { +#ifndef CONFIG_PREEMPT_RT if (!strcmp(str, "none")) return preempt_dynamic_none; if (!strcmp(str, "voluntary")) return preempt_dynamic_voluntary; +#endif if (!strcmp(str, "full")) return preempt_dynamic_full; +#ifdef CONFIG_ARCH_HAS_PREEMPT_LAZY + if (!strcmp(str, "lazy")) + return preempt_dynamic_lazy; +#endif + return -EINVAL; } +#define preempt_dynamic_key_enable(f) static_key_enable(&sk_dynamic_##f.key) +#define preempt_dynamic_key_disable(f) static_key_disable(&sk_dynamic_##f.key) + #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) #define preempt_dynamic_enable(f) static_call_update(f, f##_dynamic_enabled) #define preempt_dynamic_disable(f) static_call_update(f, f##_dynamic_disabled) #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY) -#define preempt_dynamic_enable(f) static_key_enable(&sk_dynamic_##f.key) -#define preempt_dynamic_disable(f) static_key_disable(&sk_dynamic_##f.key) +#define preempt_dynamic_enable(f) preempt_dynamic_key_enable(f) +#define preempt_dynamic_disable(f) preempt_dynamic_key_disable(f) #else #error "Unsupported PREEMPT_DYNAMIC mechanism" #endif @@ -7416,6 +7481,7 @@ static void __sched_dynamic_update(int mode) preempt_dynamic_enable(preempt_schedule); preempt_dynamic_enable(preempt_schedule_notrace); preempt_dynamic_enable(irqentry_exit_cond_resched); + preempt_dynamic_key_disable(preempt_lazy); switch (mode) { case preempt_dynamic_none: @@ -7425,6 +7491,7 @@ static void __sched_dynamic_update(int mode) preempt_dynamic_disable(preempt_schedule); preempt_dynamic_disable(preempt_schedule_notrace); preempt_dynamic_disable(irqentry_exit_cond_resched); + preempt_dynamic_key_disable(preempt_lazy); if (mode != preempt_dynamic_mode) pr_info("Dynamic Preempt: none\n"); break; @@ -7436,6 +7503,7 @@ static void __sched_dynamic_update(int mode) preempt_dynamic_disable(preempt_schedule); preempt_dynamic_disable(preempt_schedule_notrace); preempt_dynamic_disable(irqentry_exit_cond_resched); + preempt_dynamic_key_disable(preempt_lazy); if (mode != preempt_dynamic_mode) pr_info("Dynamic Preempt: voluntary\n"); break; @@ -7447,9 +7515,22 @@ static void __sched_dynamic_update(int mode) preempt_dynamic_enable(preempt_schedule); preempt_dynamic_enable(preempt_schedule_notrace); preempt_dynamic_enable(irqentry_exit_cond_resched); + preempt_dynamic_key_disable(preempt_lazy); if (mode != preempt_dynamic_mode) pr_info("Dynamic Preempt: full\n"); break; + + case preempt_dynamic_lazy: + if (!klp_override) + preempt_dynamic_disable(cond_resched); + preempt_dynamic_disable(might_resched); + preempt_dynamic_enable(preempt_schedule); + preempt_dynamic_enable(preempt_schedule_notrace); + preempt_dynamic_enable(irqentry_exit_cond_resched); + preempt_dynamic_key_enable(preempt_lazy); + if (mode != preempt_dynamic_mode) + pr_info("Dynamic Preempt: lazy\n"); + break; } preempt_dynamic_mode = mode; @@ -7512,6 +7593,8 @@ static void __init preempt_dynamic_init(void) sched_dynamic_update(preempt_dynamic_none); } else if (IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY)) { sched_dynamic_update(preempt_dynamic_voluntary); + } else if (IS_ENABLED(CONFIG_PREEMPT_LAZY)) { + sched_dynamic_update(preempt_dynamic_lazy); } else { /* Default static call setting, nothing to do */ WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT)); @@ -7532,6 +7615,7 @@ static void __init preempt_dynamic_init(void) PREEMPT_MODEL_ACCESSOR(none); PREEMPT_MODEL_ACCESSOR(voluntary); PREEMPT_MODEL_ACCESSOR(full); +PREEMPT_MODEL_ACCESSOR(lazy); #else /* !CONFIG_PREEMPT_DYNAMIC: */ diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c index f4035c7a0fa1..a48b2a701ec2 100644 --- a/kernel/sched/debug.c +++ b/kernel/sched/debug.c @@ -245,11 +245,12 @@ static ssize_t sched_dynamic_write(struct file *filp, const char __user *ubuf, static int sched_dynamic_show(struct seq_file *m, void *v) { static const char * preempt_modes[] = { - "none", "voluntary", "full" + "none", "voluntary", "full", "lazy", }; - int i; + int j = ARRAY_SIZE(preempt_modes) - !IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY); + int i = IS_ENABLED(CONFIG_PREEMPT_RT) * 2; - for (i = 0; i < ARRAY_SIZE(preempt_modes); i++) { + for (; i < j; i++) { if (preempt_dynamic_mode == i) seq_puts(m, "("); seq_puts(m, preempt_modes[i]); diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 54e7c4c3e2c5..10e9484d1d43 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1264,7 +1264,7 @@ static void update_curr(struct cfs_rq *cfs_rq) return; if (resched || did_preempt_short(cfs_rq, curr)) { - resched_curr(rq); + resched_curr_lazy(rq); clear_buddies(cfs_rq, curr); } } @@ -5691,7 +5691,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued) * validating it and just reschedule. */ if (queued) { - resched_curr(rq_of(cfs_rq)); + resched_curr_lazy(rq_of(cfs_rq)); return; } /* @@ -8855,7 +8855,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int return; preempt: - resched_curr(rq); + resched_curr_lazy(rq); } static struct task_struct *pick_task_fair(struct rq *rq) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index c5d6012794de..b5f3890f3050 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2696,6 +2696,7 @@ extern void init_sched_rt_class(void); extern void init_sched_fair_class(void); extern void resched_curr(struct rq *rq); +extern void resched_curr_lazy(struct rq *rq); extern void resched_cpu(int cpu); extern void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime); diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 6a891e00aa7f..acbed0ffe083 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2563,6 +2563,8 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status) trace_flags |= TRACE_FLAG_NEED_RESCHED; if (test_preempt_need_resched()) trace_flags |= TRACE_FLAG_PREEMPT_RESCHED; + if (IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY) && tif_test_bit(TIF_NEED_RESCHED_LAZY)) + trace_flags |= TRACE_FLAG_NEED_RESCHED_LAZY; return (trace_flags << 16) | (min_t(unsigned int, pc & 0xff, 0xf)) | (min_t(unsigned int, migration_disable_value(), 0xf)) << 4; } diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index a50ed23bee77..4a9087112526 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -1537,27 +1537,25 @@ static int run_osnoise(void) /* * In some cases, notably when running on a nohz_full CPU with - * a stopped tick PREEMPT_RCU has no way to account for QSs. - * This will eventually cause unwarranted noise as PREEMPT_RCU - * will force preemption as the means of ending the current - * grace period. We avoid this problem by calling - * rcu_momentary_eqs(), which performs a zero duration - * EQS allowing PREEMPT_RCU to end the current grace period. - * This call shouldn't be wrapped inside an RCU critical - * section. + * a stopped tick PREEMPT_RCU or PREEMPT_LAZY have no way to + * account for QSs. This will eventually cause unwarranted + * noise as RCU forces preemption as the means of ending the + * current grace period. We avoid this by calling + * rcu_momentary_eqs(), which performs a zero duration EQS + * allowing RCU to end the current grace period. This call + * shouldn't be wrapped inside an RCU critical section. * - * Note that in non PREEMPT_RCU kernels QSs are handled through - * cond_resched() + * Normally QSs for other cases are handled through cond_resched(). + * For simplicity, however, we call rcu_momentary_eqs() for all + * configurations here. */ - if (IS_ENABLED(CONFIG_PREEMPT_RCU)) { - if (!disable_irq) - local_irq_disable(); + if (!disable_irq) + local_irq_disable(); - rcu_momentary_eqs(); + rcu_momentary_eqs(); - if (!disable_irq) - local_irq_enable(); - } + if (!disable_irq) + local_irq_enable(); /* * For the non-preemptive kernel config: let threads runs, if diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index 868f2f912f28..23ca2155306b 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c @@ -460,20 +460,32 @@ int trace_print_lat_fmt(struct trace_seq *s, struct trace_entry *entry) (entry->flags & TRACE_FLAG_IRQS_OFF && bh_off) ? 'D' : (entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' : bh_off ? 'b' : - (entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' : + !IS_ENABLED(CONFIG_TRACE_IRQFLAGS_SUPPORT) ? 'X' : '.'; - switch (entry->flags & (TRACE_FLAG_NEED_RESCHED | + switch (entry->flags & (TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED)) { + case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED: + need_resched = 'B'; + break; case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_PREEMPT_RESCHED: need_resched = 'N'; break; + case TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED: + need_resched = 'L'; + break; + case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY: + need_resched = 'b'; + break; case TRACE_FLAG_NEED_RESCHED: need_resched = 'n'; break; case TRACE_FLAG_PREEMPT_RESCHED: need_resched = 'p'; break; + case TRACE_FLAG_NEED_RESCHED_LAZY: + need_resched = 'l'; + break; default: need_resched = '.'; break; -- 2.47.1