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Message-ID: <8bba6a0a8eee17e741c5155b04ff1b1c9f34bf94.1304541919.git.mst@redhat.com>
Date: Wed, 4 May 2011 23:51:47 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Rusty Russell <rusty@...tcorp.com.au>,
Carsten Otte <cotte@...ibm.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
linux390@...ibm.com, Martin Schwidefsky <schwidefsky@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Shirley Ma <xma@...ibm.com>, lguest@...ts.ozlabs.org,
linux-kernel@...r.kernel.org,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
linux-s390@...r.kernel.org, kvm@...r.kernel.org,
Krishna Kumar <krkumar2@...ibm.com>,
Tom Lendacky <tahm@...ux.vnet.ibm.com>, steved@...ibm.com,
habanero@...ux.vnet.ibm.com
Subject: [PATCH 09/18] virtio: use avail_event index
Use the new avail_event feature to reduce the number
of exits from the guest.
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
drivers/virtio/virtio_ring.c | 39 ++++++++++++++++++++++++++++++++++++++-
1 files changed, 38 insertions(+), 1 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 3a3ed75..262dfe6 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -82,6 +82,15 @@ struct vring_virtqueue
/* Host supports indirect buffers */
bool indirect;
+ /* Host publishes avail event idx */
+ bool event;
+
+ /* Is kicked_avail below valid? */
+ bool kicked_avail_valid;
+
+ /* avail idx value we already kicked. */
+ u16 kicked_avail;
+
/* Number of free buffers */
unsigned int num_free;
/* Head of free buffer list. */
@@ -228,6 +237,12 @@ add_head:
* new available array entries. */
virtio_wmb();
vq->vring.avail->idx++;
+ /* If the driver never bothers to kick in a very long while,
+ * avail index might wrap around. If that happens, invalidate
+ * kicked_avail index we stored. TODO: make sure all drivers
+ * kick at least once in 2^16 and remove this. */
+ if (unlikely(vq->vring.avail->idx == vq->kicked_avail))
+ vq->kicked_avail_valid = true;
pr_debug("Added buffer head %i to %p\n", head, vq);
END_USE(vq);
@@ -236,6 +251,23 @@ add_head:
}
EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp);
+
+static bool vring_notify(struct vring_virtqueue *vq)
+{
+ u16 old, new;
+ bool v;
+ if (!vq->event)
+ return !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
+
+ v = vq->kicked_avail_valid;
+ old = vq->kicked_avail;
+ new = vq->kicked_avail = vq->vring.avail->idx;
+ vq->kicked_avail_valid = true;
+ if (unlikely(!v))
+ return true;
+ return vring_need_event(vring_avail_event(&vq->vring), new, old);
+}
+
void virtqueue_kick(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
@@ -244,7 +276,7 @@ void virtqueue_kick(struct virtqueue *_vq)
/* Need to update avail index before checking if we should notify */
virtio_mb();
- if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
+ if (vring_notify(vq))
/* Prod other side to tell it about changes. */
vq->notify(&vq->vq);
@@ -437,6 +469,8 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
vq->vq.name = name;
vq->notify = notify;
vq->broken = false;
+ vq->kicked_avail_valid = false;
+ vq->kicked_avail = 0;
vq->last_used_idx = 0;
list_add_tail(&vq->vq.list, &vdev->vqs);
#ifdef DEBUG
@@ -444,6 +478,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
#endif
vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);
+ vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_AVAIL_EVENT_IDX);
/* No callback? Tell other side not to bother us. */
if (!callback)
@@ -482,6 +517,8 @@ void vring_transport_features(struct virtio_device *vdev)
break;
case VIRTIO_RING_F_USED_EVENT_IDX:
break;
+ case VIRTIO_RING_F_AVAIL_EVENT_IDX:
+ break;
default:
/* We don't understand this bit. */
clear_bit(i, vdev->features);
--
1.7.5.53.gc233e
--
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