[PATCH v3 1/3] KVM: make halt_poll_ns per-VCPU

[PATCH v3 1/3] KVM: make halt_poll_ns per-VCPU

[Wanpeng Li]

Change halt_poll_ns into per-VCPU variable, seeded from module parameter,
to allow greater flexibility.

Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 include/linux/kvm_host.h | 1 +
 virt/kvm/kvm_main.c      | 5 +++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 81089cf..1bef9e2 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -242,6 +242,7 @@ struct kvm_vcpu {
 	int sigset_active;
 	sigset_t sigset;
 	struct kvm_vcpu_stat stat;
+	unsigned int halt_poll_ns;
 
 #ifdef CONFIG_HAS_IOMEM
 	int mmio_needed;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d8db2f8f..c06e57c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -217,6 +217,7 @@ 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);
 
@@ -1930,8 +1931,8 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
 	bool waited = false;
 
 	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 {
 			/*
-- 
1.9.1

[PATCH v3 2/3] KVM: dynamic halt_poll_ns adjustment

[Wanpeng Li]

There is a downside of halt_poll_ns since poll is still happen for idle 
VCPU which can waste cpu usage. This patch adds the ability to adjust 
halt_poll_ns dynamically. 

There are two new kernel parameters for changing the halt_poll_ns:
halt_poll_ns_grow and halt_poll_ns_shrink. The shrink/grow matrix is 
suggested by David: 

if (poll successfully for interrupt): stay the same
  else if (length of kvm_vcpu_block is longer than halt_poll_ns_max): shrink
  else if (length of kvm_vcpu_block is less than halt_poll_ns_max): grow

Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 virt/kvm/kvm_main.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c06e57c..1ed02d1 100644
--- 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, 2ms is enough */
+static unsigned int halt_poll_ns = 2000000;
 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:
  *
@@ -1907,6 +1916,31 @@ 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 val = vcpu->halt_poll_ns;
+
+	/* 500us step */
+	if (val == 0 && halt_poll_ns_grow)
+		val = 500000;
+	else
+		val *= halt_poll_ns_grow;
+
+	vcpu->halt_poll_ns = val;
+}
+
+static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu)
+{
+	int val = vcpu->halt_poll_ns;
+
+	if (halt_poll_ns_shrink == 0)
+		val = 0;
+	else
+		val /= halt_poll_ns_shrink;
+
+	vcpu->halt_poll_ns = val;
+}
+
 static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
 {
 	if (kvm_arch_vcpu_runnable(vcpu)) {
@@ -1960,6 +1994,13 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
 	finish_wait(&vcpu->wq, &wait);
 	cur = ktime_get();
 
+	if (waited) {
+		if (vcpu->halt_poll_ns > halt_poll_ns)
+			shrink_halt_poll_ns(vcpu);
+		else
+			grow_halt_poll_ns(vcpu);
+	}
+
 out:
 	trace_kvm_vcpu_wakeup(ktime_to_ns(cur) - ktime_to_ns(start), waited);
 }
-- 
1.9.1

[PATCH v3 3/3] KVM: trace kvm_halt_poll_ns grow/shrink

[Wanpeng Li]

Tracepoint for dynamic halt_pool_ns, fired on every potential change.

Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 include/trace/events/kvm.h | 30 ++++++++++++++++++++++++++++++
 virt/kvm/kvm_main.c        |  8 ++++++--
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h
index a44062d..75ddf80 100644
--- a/include/trace/events/kvm.h
+++ b/include/trace/events/kvm.h
@@ -356,6 +356,36 @@ TRACE_EVENT(
 		  __entry->address)
 );
 
+TRACE_EVENT(kvm_halt_poll_ns,
+	TP_PROTO(bool grow, unsigned int vcpu_id, int new, int old),
+	TP_ARGS(grow, vcpu_id, new, old),
+
+	TP_STRUCT__entry(
+		__field(bool, grow)
+		__field(unsigned int, vcpu_id)
+		__field(int, new)
+		__field(int, old)
+	),
+
+	TP_fast_assign(
+		__entry->grow           = grow;
+		__entry->vcpu_id        = vcpu_id;
+		__entry->new            = new;
+		__entry->old            = old;
+	),
+
+	TP_printk("vcpu %u: halt_pool_ns %d (%s %d)",
+			__entry->vcpu_id,
+			__entry->new,
+			__entry->grow ? "grow" : "shrink",
+			__entry->old)
+);
+
+#define trace_kvm_halt_poll_ns_grow(vcpu_id, new, old) \
+	trace_kvm_halt_poll_ns(true, vcpu_id, new, old)
+#define trace_kvm_halt_poll_ns_shrink(vcpu_id, new, old) \
+	trace_kvm_halt_poll_ns(false, vcpu_id, new, old)
+
 #endif
 
 #endif /* _TRACE_KVM_MAIN_H */
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1ed02d1..a4b7eb9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1918,8 +1918,9 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_mark_page_dirty);
 
 static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 {
-	int val = vcpu->halt_poll_ns;
+	int old, val;
 
+	old = val = vcpu->halt_poll_ns;
 	/* 500us step */
 	if (val == 0 && halt_poll_ns_grow)
 		val = 500000;
@@ -1927,18 +1928,21 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 		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 val = vcpu->halt_poll_ns;
+	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)
-- 
1.9.1