[PATCH 2/2] kvm tools: Do not poll ioeventfd if vhost is enabled

[Asias He <asias.hejun@xxxxxxxxx>]

If vhost is enabled for a virtio device, vhost will poll the ioeventfd
in kernel side and there is no need to poll it in userspace. Otherwise,
both vhost kernel and userspace will race to poll.

Signed-off-by: Asias He <asias.hejun@xxxxxxxxx>
---
 tools/kvm/include/kvm/ioeventfd.h |    2 +-
 tools/kvm/ioeventfd.c             |    5 ++++-
 tools/kvm/virtio/mmio.c           |   10 +++++++++-
 tools/kvm/virtio/pci.c            |   10 +++++++++-
 4 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/tools/kvm/include/kvm/ioeventfd.h b/tools/kvm/include/kvm/ioeventfd.h
index 70cce9a..d71fa40 100644
--- a/tools/kvm/include/kvm/ioeventfd.h
+++ b/tools/kvm/include/kvm/ioeventfd.h
@@ -22,7 +22,7 @@ struct ioevent {
 
 int ioeventfd__init(struct kvm *kvm);
 int ioeventfd__exit(struct kvm *kvm);
-int ioeventfd__add_event(struct ioevent *ioevent, bool is_pio);
+int ioeventfd__add_event(struct ioevent *ioevent, bool is_pio, bool poll_in_userspace);
 int ioeventfd__del_event(u64 addr, u64 datamatch);
 
 #endif
diff --git a/tools/kvm/ioeventfd.c b/tools/kvm/ioeventfd.c
index 97deb06..226876f 100644
--- a/tools/kvm/ioeventfd.c
+++ b/tools/kvm/ioeventfd.c
@@ -117,7 +117,7 @@ int ioeventfd__exit(struct kvm *kvm)
 	return 0;
 }
 
-int ioeventfd__add_event(struct ioevent *ioevent, bool is_pio)
+int ioeventfd__add_event(struct ioevent *ioevent, bool is_pio, bool poll_in_userspace)
 {
 	struct kvm_ioeventfd kvm_ioevent;
 	struct epoll_event epoll_event;
@@ -151,6 +151,9 @@ int ioeventfd__add_event(struct ioevent *ioevent, bool is_pio)
 		goto cleanup;
 	}
 
+	if (!poll_in_userspace)
+		return 0;
+
 	epoll_event = (struct epoll_event) {
 		.events		= EPOLLIN,
 		.data.ptr	= new_ioevent,
diff --git a/tools/kvm/virtio/mmio.c b/tools/kvm/virtio/mmio.c
index 8319954..45687a6 100644
--- a/tools/kvm/virtio/mmio.c
+++ b/tools/kvm/virtio/mmio.c
@@ -48,7 +48,15 @@ static int virtio_mmio_init_ioeventfd(struct kvm *kvm,
 		.fd		= eventfd(0, 0),
 	};
 
-	err = ioeventfd__add_event(&ioevent, false);
+	if (vdev->ops->notify_vq_eventfd)
+		/*
+		 * Vhost will poll the eventfd in host kernel side,
+		 * no need to poll in userspace.
+		 */
+		err = ioeventfd__add_event(&ioevent, true, false);
+	else
+		/* Need to poll in userspace. */
+		err = ioeventfd__add_event(&ioevent, true, true);
 	if (err)
 		return err;
 
diff --git a/tools/kvm/virtio/pci.c b/tools/kvm/virtio/pci.c
index 8558341e..ef411c1 100644
--- a/tools/kvm/virtio/pci.c
+++ b/tools/kvm/virtio/pci.c
@@ -40,7 +40,15 @@ static int virtio_pci__init_ioeventfd(struct kvm *kvm, struct virtio_device *vde
 		.fd		= eventfd(0, 0),
 	};
 
-	r = ioeventfd__add_event(&ioevent, true);
+	if (vdev->ops->notify_vq_eventfd)
+		/*
+		 * Vhost will poll the eventfd in host kernel side,
+		 * no need to poll in userspace.
+		 */
+		r = ioeventfd__add_event(&ioevent, true, false);
+	else
+		/* Need to poll in userspace. */
+		r = ioeventfd__add_event(&ioevent, true, true);
 	if (r)
 		return r;
 
-- 
1.7.10.4

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