[PATCH RFC] virtio-pci: share config interrupt between virtio devices

[Amos Kong <akong@redhat.com>]

One VM only has 128 msix interrupt, virtio-config interrupt
has less workload. This patch shares one normal interrupt
for configuration between virtio devices.

Signed-off-by: Amos Kong <akong@redhat.com>
---
 drivers/virtio/virtio_pci.c | 41 ++++++++++++++++-------------------------
 1 file changed, 16 insertions(+), 25 deletions(-)

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 3d1463c..b1263b3 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -52,6 +52,7 @@ struct virtio_pci_device
 	/* Name strings for interrupts. This size should be enough,
 	 * and I'm too lazy to allocate each name separately. */
 	char (*msix_names)[256];
+	char config_msix_name[256];
 	/* Number of available vectors */
 	unsigned msix_vectors;
 	/* Vectors allocated, excluding per-vq vectors if any */
@@ -282,12 +283,6 @@ static void vp_free_vectors(struct virtio_device *vdev)
 			free_cpumask_var(vp_dev->msix_affinity_masks[i]);
 
 	if (vp_dev->msix_enabled) {
-		/* Disable the vector used for configuration */
-		iowrite16(VIRTIO_MSI_NO_VECTOR,
-			  vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
-		/* Flush the write out to device */
-		ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
-
 		pci_disable_msix(vp_dev->pci_dev);
 		vp_dev->msix_enabled = 0;
 	}
@@ -339,24 +334,18 @@ static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
 		goto error;
 	vp_dev->msix_enabled = 1;
 
-	/* Set the vector used for configuration */
-	v = vp_dev->msix_used_vectors;
-	snprintf(vp_dev->msix_names[v], sizeof *vp_dev->msix_names,
+	/* Set shared IRQ for configuration */
+	snprintf(vp_dev->config_msix_name, sizeof(*vp_dev->msix_names),
 		 "%s-config", name);
-	err = request_irq(vp_dev->msix_entries[v].vector,
-			  vp_config_changed, 0, vp_dev->msix_names[v],
+	err = request_irq(vp_dev->pci_dev->irq,
+			  vp_config_changed,
+			  IRQF_SHARED,
+			  vp_dev->config_msix_name,
 			  vp_dev);
-	if (err)
-		goto error;
-	++vp_dev->msix_used_vectors;
-
-	iowrite16(v, vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
-	/* Verify we had enough resources to assign the vector */
-	v = ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
-	if (v == VIRTIO_MSI_NO_VECTOR) {
-		err = -EBUSY;
+	if (!err)
+		vp_dev->intx_enabled = 1;
+	else
 		goto error;
-	}
 
 	if (!per_vq_vectors) {
 		/* Shared vector for all VQs */
@@ -535,14 +524,16 @@ static int vp_try_to_find_vqs(struct virtio_device *vdev, unsigned nvqs,
 			goto error_request;
 	} else {
 		if (per_vq_vectors) {
-			/* Best option: one for change interrupt, one per vq. */
-			nvectors = 1;
+			/* Best option: one normal interrupt for change,
+			   one msix per vq. */
+			nvectors = 0;
 			for (i = 0; i < nvqs; ++i)
 				if (callbacks[i])
 					++nvectors;
 		} else {
-			/* Second best: one for change, shared for all vqs. */
-			nvectors = 2;
+			/* Second best: one normal interrupt for
+			   change, share one msix for all vqs. */
+			nvectors = 1;
 		}
 
 		err = vp_request_msix_vectors(vdev, nvectors, per_vq_vectors);
-- 
1.9.3