diff options
| author | Marcelo Tosatti <mtosatti@redhat.com> | 2015-04-08 20:33:24 -0300 |
|---|---|---|
| committer | Anders Roxell <anders.roxell@linaro.org> | 2015-06-26 22:31:47 +0200 |
| commit | 3bc2aab41a690da5bcada9a54b17323490b62cbf (patch) | |
| tree | 737ac23e585745fc7a6ce05e1ca25393622d87dd /arch/powerpc | |
| parent | 9f1a2fabc867753bc7998c4fcb4ef2d362ffb644 (diff) | |
KVM: use simple waitqueue for vcpu->wq
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: stable-rt@vger.kernel.org
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'arch/powerpc')
| -rw-r--r-- | arch/powerpc/include/asm/kvm_host.h | 4 | ||||
| -rw-r--r-- | arch/powerpc/kvm/book3s_hv.c | 20 |
2 files changed, 12 insertions, 12 deletions
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); } } |