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kvm tools: Support virtio indirect buffers

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Indirect buffers are ring descriptors which point to more (even more)
descriptors.

This can be used to increase the effective ring capacity, which helps the
guest to batch large requests - very useful for blk devices.

This patch also enables indirect buffers for virtio-net and virtio-blk.

The patch is based on the lguest's code which does the same.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
This commit is contained in:
Sasha Levin
2011-11-28 19:54:27 +02:00
committed by Will Deacon
parent 2fddfdb536
commit 754c8ce330
3 changed files with 42 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files
virtio/blk.c
+2 -1
View File
@@ -148,7 +148,8 @@ static u32 get_host_features(struct kvm *kvm, void *dev)
{
return 1UL << VIRTIO_BLK_F_SEG_MAX
| 1UL << VIRTIO_BLK_F_FLUSH
| 1UL << VIRTIO_RING_F_EVENT_IDX;
| 1UL << VIRTIO_RING_F_EVENT_IDX
| 1UL << VIRTIO_RING_F_INDIRECT_DESC;
}
static void set_guest_features(struct kvm *kvm, void *dev, u32 features)
virtio/core.c
+38 -9
View File
@@ -33,27 +33,56 @@ struct vring_used_elem *virt_queue__set_used_elem(struct virt_queue *queue, u32
return used_elem;
}
/*
* Each buffer in the virtqueues is actually a chain of descriptors. This
* function returns the next descriptor in the chain, or vq->vring.num if we're
* at the end.
*/
static unsigned next_desc(struct vring_desc *desc,
unsigned int i, unsigned int max)
{
unsigned int next;
/* If this descriptor says it doesn't chain, we're done. */
if (!(desc[i].flags & VRING_DESC_F_NEXT))
return max;
/* Check they're not leading us off end of descriptors. */
next = desc[i].next;
/* Make sure compiler knows to grab that: we don't want it changing! */
wmb();
return next;
}
u16 virt_queue__get_head_iov(struct virt_queue *vq, struct iovec iov[], u16 *out, u16 *in, u16 head, struct kvm *kvm)
{
struct vring_desc *desc;
u16 idx;
u16 max;
idx = head;
*out = *in = 0;
max = vq->vring.num;
desc = vq->vring.desc;
if (desc[idx].flags & VRING_DESC_F_INDIRECT) {
max = desc[idx].len / sizeof(struct vring_desc);
desc = guest_flat_to_host(kvm, desc[idx].addr);
idx = 0;
}
do {
desc = virt_queue__get_desc(vq, idx);
iov[*out + *in].iov_base = guest_flat_to_host(kvm, desc->addr);
iov[*out + *in].iov_len = desc->len;
if (desc->flags & VRING_DESC_F_WRITE)
/* Grab the first descriptor, and check it's OK. */
iov[*out + *in].iov_len = desc[idx].len;
iov[*out + *in].iov_base = guest_flat_to_host(kvm, desc[idx].addr);
/* If this is an input descriptor, increment that count. */
if (desc[idx].flags & VRING_DESC_F_WRITE)
(*in)++;
else
(*out)++;
if (desc->flags & VRING_DESC_F_NEXT)
idx = desc->next;
else
break;
} while (1);
} while ((idx = next_desc(desc, idx, max)) != max);
return head;
}
virtio/net.c
+2 -1
View File
@@ -318,7 +318,8 @@ static u32 get_host_features(struct kvm *kvm, void *dev)
| 1UL << VIRTIO_NET_F_GUEST_UFO
| 1UL << VIRTIO_NET_F_GUEST_TSO4
| 1UL << VIRTIO_NET_F_GUEST_TSO6
| 1UL << VIRTIO_RING_F_EVENT_IDX;
| 1UL << VIRTIO_RING_F_EVENT_IDX
| 1UL << VIRTIO_RING_F_INDIRECT_DESC;
}
static void set_guest_features(struct kvm *kvm, void *dev, u32 features)