virtio: introduce an API to set affinity for a virtqueue

Sometimes, virtio device need to configure irq affinity hint to maximize the
performance. Instead of just exposing the irq of a virtqueue, this patch
introduce an API to set the affinity for a virtqueue.

The api is best-effort, the affinity hint may not be set as expected due to
platform support, irq sharing or irq type. Currently, only pci method were
implemented and we set the affinity according to:

- if device uses INTX, we just ignore the request
- if device has per vq vector, we force the affinity hint
- if the virtqueues share MSI, make the affinity OR over all affinities
  requested

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index fc457f452f64..2c4a9895379d 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -98,6 +98,7 @@
  *	vdev: the virtio_device
  *      This returns a pointer to the bus name a la pci_name from which
  *      the caller can then copy.
+ * @set_vq_affinity: set the affinity for a virtqueue.
  */
 typedef void vq_callback_t(struct virtqueue *);
 struct virtio_config_ops {
@@ -116,6 +117,7 @@ struct virtio_config_ops {
 	u32 (*get_features)(struct virtio_device *vdev);
 	void (*finalize_features)(struct virtio_device *vdev);
 	const char *(*bus_name)(struct virtio_device *vdev);
+	int (*set_vq_affinity)(struct virtqueue *vq, int cpu);
 };
 
 /* If driver didn't advertise the feature, it will never appear. */
@@ -190,5 +192,24 @@ const char *virtio_bus_name(struct virtio_device *vdev)
 	return vdev->config->bus_name(vdev);
 }
 
+/**
+ * virtqueue_set_affinity - setting affinity for a virtqueue
+ * @vq: the virtqueue
+ * @cpu: the cpu no.
+ *
+ * Pay attention the function are best-effort: the affinity hint may not be set
+ * due to config support, irq type and sharing.
+ *
+ */
+static inline
+int virtqueue_set_affinity(struct virtqueue *vq, int cpu)
+{
+	struct virtio_device *vdev = vq->vdev;
+	if (vdev->config->set_vq_affinity)
+		return vdev->config->set_vq_affinity(vq, cpu);
+	return 0;
+}
+
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_VIRTIO_CONFIG_H */