3.14.39-rt38-rc1 stable review patch. If anyone has any objections, please let me know.
------------------ From: Marcelo Tosatti <[email protected]> The problem: On -RT, an emulated LAPIC timer instances has the following path: 1) hard interrupt 2) ksoftirqd is scheduled 3) ksoftirqd wakes up vcpu thread 4) vcpu thread is scheduled This extra context switch introduces unnecessary latency in the LAPIC path for a KVM guest. The solution: Allow waking up vcpu thread from hardirq context, thus avoiding the need for ksoftirqd to be scheduled. Normal waitqueues make use of spinlocks, which on -RT are sleepable locks. Therefore, waking up a waitqueue waiter involves locking a sleeping lock, which is not allowed from hard interrupt context. cyclictest command line: This patch reduces the average latency in my tests from 14us to 11us. Cc: [email protected] Signed-off-by: Marcelo Tosatti <[email protected]> Signed-off-by: Sebastian Andrzej Siewior <[email protected]> Signed-off-by: Steven Rostedt <[email protected]> --- arch/arm/kvm/arm.c | 4 ++-- arch/arm/kvm/psci.c | 4 ++-- arch/powerpc/include/asm/kvm_host.h | 4 ++-- arch/powerpc/kvm/book3s_hv.c | 20 ++++++++++---------- arch/s390/include/asm/kvm_host.h | 2 +- arch/x86/kvm/lapic.c | 6 +++--- include/linux/kvm_host.h | 4 ++-- virt/kvm/async_pf.c | 4 ++-- virt/kvm/kvm_main.c | 16 ++++++++-------- 9 files changed, 32 insertions(+), 32 deletions(-) diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c index bd18bb8b2770..9100f8a609a2 100644 --- a/arch/arm/kvm/arm.c +++ b/arch/arm/kvm/arm.c @@ -495,9 +495,9 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu) static void vcpu_pause(struct kvm_vcpu *vcpu) { - wait_queue_head_t *wq = kvm_arch_vcpu_wq(vcpu); + struct swait_head *wq = kvm_arch_vcpu_wq(vcpu); - wait_event_interruptible(*wq, !vcpu->arch.pause); + swait_event_interruptible(*wq, !vcpu->arch.pause); } static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu) diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c index 448f60e8d23c..19c6c9c2118c 100644 --- a/arch/arm/kvm/psci.c +++ b/arch/arm/kvm/psci.c @@ -36,7 +36,7 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu) { struct kvm *kvm = source_vcpu->kvm; struct kvm_vcpu *vcpu = NULL, *tmp; - wait_queue_head_t *wq; + struct swait_head *wq; unsigned long cpu_id; unsigned long mpidr; phys_addr_t target_pc; @@ -80,7 +80,7 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu) smp_mb(); /* Make sure the above is visible */ wq = kvm_arch_vcpu_wq(vcpu); - wake_up_interruptible(wq); + swait_wake_interruptible(wq); return KVM_PSCI_RET_SUCCESS; } diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h index 1eaea2dea174..dfaf2c2d8e7f 100644 --- a/arch/powerpc/include/asm/kvm_host.h +++ b/arch/powerpc/include/asm/kvm_host.h @@ -295,7 +295,7 @@ struct kvmppc_vcore { u8 in_guest; struct list_head runnable_threads; spinlock_t lock; - wait_queue_head_t wq; + struct swait_head wq; u64 stolen_tb; u64 preempt_tb; struct kvm_vcpu *runner; @@ -612,7 +612,7 @@ struct kvm_vcpu_arch { u8 prodded; u32 last_inst; - wait_queue_head_t *wqp; + struct swait_head *wqp; struct kvmppc_vcore *vcore; int ret; int trap; diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 7a25d9218a05..0019281510da 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -74,11 +74,11 @@ static void kvmppc_fast_vcpu_kick_hv(struct kvm_vcpu *vcpu) { int me; int cpu = vcpu->cpu; - wait_queue_head_t *wqp; + struct swait_head *wqp; wqp = kvm_arch_vcpu_wq(vcpu); - if (waitqueue_active(wqp)) { - wake_up_interruptible(wqp); + if (swaitqueue_active(wqp)) { + swait_wake_interruptible(wqp); ++vcpu->stat.halt_wakeup; } @@ -583,8 +583,8 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu) tvcpu->arch.prodded = 1; smp_mb(); if (vcpu->arch.ceded) { - if (waitqueue_active(&vcpu->wq)) { - wake_up_interruptible(&vcpu->wq); + if (swaitqueue_active(&vcpu->wq)) { + swait_wake_interruptible(&vcpu->wq); vcpu->stat.halt_wakeup++; } } @@ -1199,7 +1199,7 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm, if (vcore) { INIT_LIST_HEAD(&vcore->runnable_threads); spin_lock_init(&vcore->lock); - init_waitqueue_head(&vcore->wq); + init_swait_head(&vcore->wq); vcore->preempt_tb = TB_NIL; vcore->lpcr = kvm->arch.lpcr; vcore->first_vcpuid = core * threads_per_core; @@ -1566,13 +1566,13 @@ static void kvmppc_wait_for_exec(struct kvm_vcpu *vcpu, int wait_state) */ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc) { - DEFINE_WAIT(wait); + DEFINE_SWAITER(wait); - prepare_to_wait(&vc->wq, &wait, TASK_INTERRUPTIBLE); + swait_prepare(&vc->wq, &wait, TASK_INTERRUPTIBLE); vc->vcore_state = VCORE_SLEEPING; spin_unlock(&vc->lock); schedule(); - finish_wait(&vc->wq, &wait); + swait_finish(&vc->wq, &wait); spin_lock(&vc->lock); vc->vcore_state = VCORE_INACTIVE; } @@ -1613,7 +1613,7 @@ static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu) kvmppc_create_dtl_entry(vcpu, vc); kvmppc_start_thread(vcpu); } else if (vc->vcore_state == VCORE_SLEEPING) { - wake_up(&vc->wq); + swait_wake(&vc->wq); } } diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h index eef3dd3fd9a9..65402d300a26 100644 --- a/arch/s390/include/asm/kvm_host.h +++ b/arch/s390/include/asm/kvm_host.h @@ -233,7 +233,7 @@ struct kvm_s390_local_interrupt { atomic_t active; struct kvm_s390_float_interrupt *float_int; int timer_due; /* event indicator for waitqueue below */ - wait_queue_head_t *wq; + struct swait_head *wq; atomic_t *cpuflags; unsigned int action_bits; }; diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 6326cce914ab..8b25d010d5e4 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1567,7 +1567,7 @@ static enum hrtimer_restart apic_timer_fn(struct hrtimer *data) struct kvm_timer *ktimer = container_of(data, struct kvm_timer, timer); struct kvm_lapic *apic = container_of(ktimer, struct kvm_lapic, lapic_timer); struct kvm_vcpu *vcpu = apic->vcpu; - wait_queue_head_t *q = &vcpu->wq; + struct swait_head *q = &vcpu->wq; /* * There is a race window between reading and incrementing, but we do @@ -1581,8 +1581,8 @@ static enum hrtimer_restart apic_timer_fn(struct hrtimer *data) kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu); } - if (waitqueue_active(q)) - wake_up_interruptible(q); + if (swaitqueue_active(q)) + swait_wake_interruptible(q); if (lapic_is_periodic(apic)) { hrtimer_add_expires_ns(&ktimer->timer, ktimer->period); diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index b8e9a43e501a..aebf20c9bfab 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -231,7 +231,7 @@ struct kvm_vcpu { int fpu_active; int guest_fpu_loaded, guest_xcr0_loaded; - wait_queue_head_t wq; + struct swait_head wq; struct pid *pid; int sigset_active; sigset_t sigset; @@ -677,7 +677,7 @@ static inline bool kvm_arch_has_noncoherent_dma(struct kvm *kvm) } #endif -static inline wait_queue_head_t *kvm_arch_vcpu_wq(struct kvm_vcpu *vcpu) +static inline struct swait_head *kvm_arch_vcpu_wq(struct kvm_vcpu *vcpu) { #ifdef __KVM_HAVE_ARCH_WQP return vcpu->arch.wqp; diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c index f2c80d5451c3..10634baf3b08 100644 --- a/virt/kvm/async_pf.c +++ b/virt/kvm/async_pf.c @@ -82,8 +82,8 @@ static void async_pf_execute(struct work_struct *work) trace_kvm_async_pf_completed(addr, gva); - if (waitqueue_active(&vcpu->wq)) - wake_up_interruptible(&vcpu->wq); + if (swaitqueue_active(&vcpu->wq)) + swait_wake_interruptible(&vcpu->wq); mmput(mm); kvm_put_kvm(vcpu->kvm); diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 66112533b1e9..38a0d7a5ce74 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -219,7 +219,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id) vcpu->kvm = kvm; vcpu->vcpu_id = id; vcpu->pid = NULL; - init_waitqueue_head(&vcpu->wq); + init_swait_head(&vcpu->wq); kvm_async_pf_vcpu_init(vcpu); page = alloc_page(GFP_KERNEL | __GFP_ZERO); @@ -1675,10 +1675,10 @@ EXPORT_SYMBOL_GPL(mark_page_dirty); */ void kvm_vcpu_block(struct kvm_vcpu *vcpu) { - DEFINE_WAIT(wait); + DEFINE_SWAITER(wait); for (;;) { - prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE); + swait_prepare(&vcpu->wq, &wait, TASK_INTERRUPTIBLE); if (kvm_arch_vcpu_runnable(vcpu)) { kvm_make_request(KVM_REQ_UNHALT, vcpu); @@ -1692,7 +1692,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) schedule(); } - finish_wait(&vcpu->wq, &wait); + swait_finish(&vcpu->wq, &wait); } EXPORT_SYMBOL_GPL(kvm_vcpu_block); @@ -1704,11 +1704,11 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu) { int me; int cpu = vcpu->cpu; - wait_queue_head_t *wqp; + struct swait_head *wqp; wqp = kvm_arch_vcpu_wq(vcpu); - if (waitqueue_active(wqp)) { - wake_up_interruptible(wqp); + if (swaitqueue_active(wqp)) { + swait_wake_interruptible(wqp); ++vcpu->stat.halt_wakeup; } @@ -1814,7 +1814,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) continue; if (vcpu == me) continue; - if (waitqueue_active(&vcpu->wq)) + if (swaitqueue_active(&vcpu->wq)) continue; if (!kvm_vcpu_eligible_for_directed_yield(vcpu)) continue; -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
