From cfd8983f03c7b2f977faab8dfc4ec5f6dbf9c1f3 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 18 May 2016 20:43:02 +0200 Subject: x86, locking/spinlocks: Remove ticket (spin)lock implementation We've unconditionally used the queued spinlock for many releases now. Its time to remove the old ticket lock code. Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Waiman Long Cc: Waiman.Long@hpe.com Cc: david.vrabel@citrix.com Cc: dhowells@redhat.com Cc: pbonzini@redhat.com Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/20160518184302.GO3193@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- arch/x86/kernel/kvm.c | 245 ----------------------------------- arch/x86/kernel/paravirt-spinlocks.c | 7 - arch/x86/kernel/paravirt_patch_32.c | 4 +- arch/x86/kernel/paravirt_patch_64.c | 4 +- 4 files changed, 4 insertions(+), 256 deletions(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 1726c4c12336..865058d087ac 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -575,9 +575,6 @@ static void kvm_kick_cpu(int cpu) kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid); } - -#ifdef CONFIG_QUEUED_SPINLOCKS - #include static void kvm_wait(u8 *ptr, u8 val) @@ -606,243 +603,6 @@ out: local_irq_restore(flags); } -#else /* !CONFIG_QUEUED_SPINLOCKS */ - -enum kvm_contention_stat { - TAKEN_SLOW, - TAKEN_SLOW_PICKUP, - RELEASED_SLOW, - RELEASED_SLOW_KICKED, - NR_CONTENTION_STATS -}; - -#ifdef CONFIG_KVM_DEBUG_FS -#define HISTO_BUCKETS 30 - -static struct kvm_spinlock_stats -{ - u32 contention_stats[NR_CONTENTION_STATS]; - u32 histo_spin_blocked[HISTO_BUCKETS+1]; - u64 time_blocked; -} spinlock_stats; - -static u8 zero_stats; - -static inline void check_zero(void) -{ - u8 ret; - u8 old; - - old = READ_ONCE(zero_stats); - if (unlikely(old)) { - ret = cmpxchg(&zero_stats, old, 0); - /* This ensures only one fellow resets the stat */ - if (ret == old) - memset(&spinlock_stats, 0, sizeof(spinlock_stats)); - } -} - -static inline void add_stats(enum kvm_contention_stat var, u32 val) -{ - check_zero(); - spinlock_stats.contention_stats[var] += val; -} - - -static inline u64 spin_time_start(void) -{ - return sched_clock(); -} - -static void __spin_time_accum(u64 delta, u32 *array) -{ - unsigned index; - - index = ilog2(delta); - check_zero(); - - if (index < HISTO_BUCKETS) - array[index]++; - else - array[HISTO_BUCKETS]++; -} - -static inline void spin_time_accum_blocked(u64 start) -{ - u32 delta; - - delta = sched_clock() - start; - __spin_time_accum(delta, spinlock_stats.histo_spin_blocked); - spinlock_stats.time_blocked += delta; -} - -static struct dentry *d_spin_debug; -static struct dentry *d_kvm_debug; - -static struct dentry *kvm_init_debugfs(void) -{ - d_kvm_debug = debugfs_create_dir("kvm-guest", NULL); - if (!d_kvm_debug) - printk(KERN_WARNING "Could not create 'kvm' debugfs directory\n"); - - return d_kvm_debug; -} - -static int __init kvm_spinlock_debugfs(void) -{ - struct dentry *d_kvm; - - d_kvm = kvm_init_debugfs(); - if (d_kvm == NULL) - return -ENOMEM; - - d_spin_debug = debugfs_create_dir("spinlocks", d_kvm); - - debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats); - - debugfs_create_u32("taken_slow", 0444, d_spin_debug, - &spinlock_stats.contention_stats[TAKEN_SLOW]); - debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug, - &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]); - - debugfs_create_u32("released_slow", 0444, d_spin_debug, - &spinlock_stats.contention_stats[RELEASED_SLOW]); - debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug, - &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]); - - debugfs_create_u64("time_blocked", 0444, d_spin_debug, - &spinlock_stats.time_blocked); - - debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug, - spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1); - - return 0; -} -fs_initcall(kvm_spinlock_debugfs); -#else /* !CONFIG_KVM_DEBUG_FS */ -static inline void add_stats(enum kvm_contention_stat var, u32 val) -{ -} - -static inline u64 spin_time_start(void) -{ - return 0; -} - -static inline void spin_time_accum_blocked(u64 start) -{ -} -#endif /* CONFIG_KVM_DEBUG_FS */ - -struct kvm_lock_waiting { - struct arch_spinlock *lock; - __ticket_t want; -}; - -/* cpus 'waiting' on a spinlock to become available */ -static cpumask_t waiting_cpus; - -/* Track spinlock on which a cpu is waiting */ -static DEFINE_PER_CPU(struct kvm_lock_waiting, klock_waiting); - -__visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want) -{ - struct kvm_lock_waiting *w; - int cpu; - u64 start; - unsigned long flags; - __ticket_t head; - - if (in_nmi()) - return; - - w = this_cpu_ptr(&klock_waiting); - cpu = smp_processor_id(); - start = spin_time_start(); - - /* - * Make sure an interrupt handler can't upset things in a - * partially setup state. - */ - local_irq_save(flags); - - /* - * The ordering protocol on this is that the "lock" pointer - * may only be set non-NULL if the "want" ticket is correct. - * If we're updating "want", we must first clear "lock". - */ - w->lock = NULL; - smp_wmb(); - w->want = want; - smp_wmb(); - w->lock = lock; - - add_stats(TAKEN_SLOW, 1); - - /* - * This uses set_bit, which is atomic but we should not rely on its - * reordering gurantees. So barrier is needed after this call. - */ - cpumask_set_cpu(cpu, &waiting_cpus); - - barrier(); - - /* - * Mark entry to slowpath before doing the pickup test to make - * sure we don't deadlock with an unlocker. - */ - __ticket_enter_slowpath(lock); - - /* make sure enter_slowpath, which is atomic does not cross the read */ - smp_mb__after_atomic(); - - /* - * check again make sure it didn't become free while - * we weren't looking. - */ - head = READ_ONCE(lock->tickets.head); - if (__tickets_equal(head, want)) { - add_stats(TAKEN_SLOW_PICKUP, 1); - goto out; - } - - /* - * halt until it's our turn and kicked. Note that we do safe halt - * for irq enabled case to avoid hang when lock info is overwritten - * in irq spinlock slowpath and no spurious interrupt occur to save us. - */ - if (arch_irqs_disabled_flags(flags)) - halt(); - else - safe_halt(); - -out: - cpumask_clear_cpu(cpu, &waiting_cpus); - w->lock = NULL; - local_irq_restore(flags); - spin_time_accum_blocked(start); -} -PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning); - -/* Kick vcpu waiting on @lock->head to reach value @ticket */ -static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket) -{ - int cpu; - - add_stats(RELEASED_SLOW, 1); - for_each_cpu(cpu, &waiting_cpus) { - const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu); - if (READ_ONCE(w->lock) == lock && - READ_ONCE(w->want) == ticket) { - add_stats(RELEASED_SLOW_KICKED, 1); - kvm_kick_cpu(cpu); - break; - } - } -} - -#endif /* !CONFIG_QUEUED_SPINLOCKS */ - /* * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present. */ @@ -854,16 +614,11 @@ void __init kvm_spinlock_init(void) if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) return; -#ifdef CONFIG_QUEUED_SPINLOCKS __pv_init_lock_hash(); pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock); pv_lock_ops.wait = kvm_wait; pv_lock_ops.kick = kvm_kick_cpu; -#else /* !CONFIG_QUEUED_SPINLOCKS */ - pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning); - pv_lock_ops.unlock_kick = kvm_unlock_kick; -#endif } static __init int kvm_spinlock_init_jump(void) diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c index 1939a0269377..2c55a003b793 100644 --- a/arch/x86/kernel/paravirt-spinlocks.c +++ b/arch/x86/kernel/paravirt-spinlocks.c @@ -8,7 +8,6 @@ #include -#ifdef CONFIG_QUEUED_SPINLOCKS __visible void __native_queued_spin_unlock(struct qspinlock *lock) { native_queued_spin_unlock(lock); @@ -21,19 +20,13 @@ bool pv_is_native_spin_unlock(void) return pv_lock_ops.queued_spin_unlock.func == __raw_callee_save___native_queued_spin_unlock; } -#endif struct pv_lock_ops pv_lock_ops = { #ifdef CONFIG_SMP -#ifdef CONFIG_QUEUED_SPINLOCKS .queued_spin_lock_slowpath = native_queued_spin_lock_slowpath, .queued_spin_unlock = PV_CALLEE_SAVE(__native_queued_spin_unlock), .wait = paravirt_nop, .kick = paravirt_nop, -#else /* !CONFIG_QUEUED_SPINLOCKS */ - .lock_spinning = __PV_IS_CALLEE_SAVE(paravirt_nop), - .unlock_kick = paravirt_nop, -#endif /* !CONFIG_QUEUED_SPINLOCKS */ #endif /* SMP */ }; EXPORT_SYMBOL(pv_lock_ops); diff --git a/arch/x86/kernel/paravirt_patch_32.c b/arch/x86/kernel/paravirt_patch_32.c index 158dc0650d5d..920c6ae08592 100644 --- a/arch/x86/kernel/paravirt_patch_32.c +++ b/arch/x86/kernel/paravirt_patch_32.c @@ -10,7 +10,7 @@ DEF_NATIVE(pv_mmu_ops, write_cr3, "mov %eax, %cr3"); DEF_NATIVE(pv_mmu_ops, read_cr3, "mov %cr3, %eax"); DEF_NATIVE(pv_cpu_ops, clts, "clts"); -#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUED_SPINLOCKS) +#if defined(CONFIG_PARAVIRT_SPINLOCKS) DEF_NATIVE(pv_lock_ops, queued_spin_unlock, "movb $0, (%eax)"); #endif @@ -49,7 +49,7 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf, PATCH_SITE(pv_mmu_ops, read_cr3); PATCH_SITE(pv_mmu_ops, write_cr3); PATCH_SITE(pv_cpu_ops, clts); -#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUED_SPINLOCKS) +#if defined(CONFIG_PARAVIRT_SPINLOCKS) case PARAVIRT_PATCH(pv_lock_ops.queued_spin_unlock): if (pv_is_native_spin_unlock()) { start = start_pv_lock_ops_queued_spin_unlock; diff --git a/arch/x86/kernel/paravirt_patch_64.c b/arch/x86/kernel/paravirt_patch_64.c index e70087a04cc8..bb3840cedb4f 100644 --- a/arch/x86/kernel/paravirt_patch_64.c +++ b/arch/x86/kernel/paravirt_patch_64.c @@ -19,7 +19,7 @@ DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs"); DEF_NATIVE(, mov32, "mov %edi, %eax"); DEF_NATIVE(, mov64, "mov %rdi, %rax"); -#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUED_SPINLOCKS) +#if defined(CONFIG_PARAVIRT_SPINLOCKS) DEF_NATIVE(pv_lock_ops, queued_spin_unlock, "movb $0, (%rdi)"); #endif @@ -61,7 +61,7 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf, PATCH_SITE(pv_cpu_ops, clts); PATCH_SITE(pv_mmu_ops, flush_tlb_single); PATCH_SITE(pv_cpu_ops, wbinvd); -#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUED_SPINLOCKS) +#if defined(CONFIG_PARAVIRT_SPINLOCKS) case PARAVIRT_PATCH(pv_lock_ops.queued_spin_unlock): if (pv_is_native_spin_unlock()) { start = start_pv_lock_ops_queued_spin_unlock; -- cgit v1.2.3