KVM: trace kvm_halt_poll_ns grow/shrink

[deliverable/linux.git] / virt / kvm / kvm_main.c

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8dc4828f623f15259c95bf9c745c37566358fe58..4662a8877f6c7a06b81803d417e52120a009a15b 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -66,9 +66,18 @@
 MODULE_AUTHOR("Qumranet");
 MODULE_LICENSE("GPL");
 
-static unsigned int halt_poll_ns;
+/* halt polling only reduces halt latency by 5-7 us, 500us is enough */
+static unsigned int halt_poll_ns = 500000;
 module_param(halt_poll_ns, uint, S_IRUGO | S_IWUSR);
 
+/* Default doubles per-vcpu halt_poll_ns. */
+static unsigned int halt_poll_ns_grow = 2;
+module_param(halt_poll_ns_grow, int, S_IRUGO);
+
+/* Default resets per-vcpu halt_poll_ns . */
+static unsigned int halt_poll_ns_shrink;
+module_param(halt_poll_ns_shrink, int, S_IRUGO);
+
 /*
  * Ordering of locks:
  *
@@ -217,6 +226,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
        vcpu->kvm = kvm;
        vcpu->vcpu_id = id;
        vcpu->pid = NULL;
+       vcpu->halt_poll_ns = 0;
        init_waitqueue_head(&vcpu->wq);
        kvm_async_pf_vcpu_init(vcpu);
 
@@ -1906,6 +1916,35 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn)
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_mark_page_dirty);
 
+static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
+{
+       int old, val;
+
+       old = val = vcpu->halt_poll_ns;
+       /* 10us base */
+       if (val == 0 && halt_poll_ns_grow)
+               val = 10000;
+       else
+               val *= halt_poll_ns_grow;
+
+       vcpu->halt_poll_ns = val;
+       trace_kvm_halt_poll_ns_grow(vcpu->vcpu_id, val, old);
+}
+
+static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu)
+{
+       int old, val;
+
+       old = val = vcpu->halt_poll_ns;
+       if (halt_poll_ns_shrink == 0)
+               val = 0;
+       else
+               val /= halt_poll_ns_shrink;
+
+       vcpu->halt_poll_ns = val;
+       trace_kvm_halt_poll_ns_shrink(vcpu->vcpu_id, val, old);
+}
+
 static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
 {
        if (kvm_arch_vcpu_runnable(vcpu)) {
@@ -1928,10 +1967,11 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
        ktime_t start, cur;
        DEFINE_WAIT(wait);
        bool waited = false;
+       u64 block_ns;
 
        start = cur = ktime_get();
-       if (halt_poll_ns) {
-               ktime_t stop = ktime_add_ns(ktime_get(), halt_poll_ns);
+       if (vcpu->halt_poll_ns) {
+               ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
 
                do {
                        /*
@@ -1960,7 +2000,21 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
        cur = ktime_get();
 
 out:
-       trace_kvm_vcpu_wakeup(ktime_to_ns(cur) - ktime_to_ns(start), waited);
+       block_ns = ktime_to_ns(cur) - ktime_to_ns(start);
+
+       if (halt_poll_ns) {
+               if (block_ns <= vcpu->halt_poll_ns)
+                       ;
+               /* we had a long block, shrink polling */
+               else if (vcpu->halt_poll_ns && block_ns > halt_poll_ns)
+                       shrink_halt_poll_ns(vcpu);
+               /* we had a short halt and our poll time is too small */
+               else if (vcpu->halt_poll_ns < halt_poll_ns &&
+                       block_ns < halt_poll_ns)
+                       grow_halt_poll_ns(vcpu);
+       }
+
+       trace_kvm_vcpu_wakeup(block_ns, waited);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_block);
 
@@ -2206,6 +2260,11 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
        }
 
        kvm->vcpus[atomic_read(&kvm->online_vcpus)] = vcpu;
+
+       /*
+        * Pairs with smp_rmb() in kvm_get_vcpu.  Write kvm->vcpus
+        * before kvm->online_vcpu's incremented value.
+        */
        smp_wmb();
        atomic_inc(&kvm->online_vcpus);