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| author | Marcelo Tosatti <mtosatti@redhat.com> | 2015-04-08 20:33:24 -0300 |
|---|---|---|
| committer | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2015-01-01 00:00:00 +0100 |
| commit | f9a205b895a7090cb8a73824129055af7204496b (patch) | |
| tree | afdd2c50131d80da2bb9325ee8b727751022d242 /virt/kvm/kvm_main.c | |
| parent | 82ed7e947b70dc6526a213cb7ec94a2c7bebec16 (diff) | |
| download | linux-rt-f9a205b895a7090cb8a73824129055af7204496b.tar.gz | |
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:
# cyclictest -m -n -q -p99 -l 1000000 -h60 -D 1m
This patch reduces the average latency in my tests from 14us to 11us.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Diffstat (limited to 'virt/kvm/kvm_main.c')
| -rw-r--r-- | virt/kvm/kvm_main.c | 16 |
1 files changed, 8 insertions, 8 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 90977418aeb6..de930768a858 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -218,7 +218,7 @@ 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); @@ -1779,7 +1779,7 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu) void kvm_vcpu_block(struct kvm_vcpu *vcpu) { ktime_t start, cur; - DEFINE_WAIT(wait); + DEFINE_SWAITER(wait); bool waited = false; start = cur = ktime_get(); @@ -1800,7 +1800,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) } for (;;) { - prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE); + swait_prepare(&vcpu->wq, &wait, TASK_INTERRUPTIBLE); if (kvm_vcpu_check_block(vcpu) < 0) break; @@ -1809,7 +1809,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) schedule(); } - finish_wait(&vcpu->wq, &wait); + swait_finish(&vcpu->wq, &wait); cur = ktime_get(); out: @@ -1825,11 +1825,11 @@ 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; } @@ -1930,7 +1930,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) continue; if (vcpu == me) continue; - if (waitqueue_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu)) + if (swaitqueue_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu)) continue; if (!kvm_vcpu_eligible_for_directed_yield(vcpu)) continue; |