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virtio: combine write of an entry into used ring 

Fill in an element of the used ring with a single combined access to the
guest physical memory, rather than using two separated accesses.
This reduces the overhead due to expensive address translation.

Signed-off-by: Vincenzo Maffione <v.maffione@gmail.com>
Message-Id: <e4a89a767a4a92cbb6bcc551e151487eb36e1722.1450218353.git.v.maffione@gmail.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Vincenzo Maffione 2016-01-31 11:29:06 +01:00 committed by Michael S. Tsirkin
parent be1fea9bc2
commit 1cdd2ee54a
1 changed files with 12 additions and 13 deletions
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25
hw/virtio/virtio.c
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@ -153,18 +153,15 @@ static inline uint16_t vring_get_used_event(VirtQueue *vq)
return vring_avail_ring(vq, vq->vring.num);
}
static inline void vring_used_ring_id(VirtQueue *vq, int i, uint32_t val)
static inline void vring_used_write(VirtQueue *vq, VRingUsedElem *uelem,
int i)
{
hwaddr pa;
pa = vq->vring.used + offsetof(VRingUsed, ring[i].id);
virtio_stl_phys(vq->vdev, pa, val);
}
static inline void vring_used_ring_len(VirtQueue *vq, int i, uint32_t val)
{
hwaddr pa;
pa = vq->vring.used + offsetof(VRingUsed, ring[i].len);
virtio_stl_phys(vq->vdev, pa, val);
virtio_tswap32s(vq->vdev, &uelem->id);
virtio_tswap32s(vq->vdev, &uelem->len);
pa = vq->vring.used + offsetof(VRingUsed, ring[i]);
address_space_write(&address_space_memory, pa, MEMTXATTRS_UNSPECIFIED,
(void *)uelem, sizeof(VRingUsedElem));
}
static uint16_t vring_used_idx(VirtQueue *vq)
@ -273,15 +270,17 @@ void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem,
void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len, unsigned int idx)
{
VRingUsedElem uelem;
trace_virtqueue_fill(vq, elem, len, idx);
virtqueue_unmap_sg(vq, elem, len);
idx = (idx + vq->used_idx) % vq->vring.num;
/* Get a pointer to the next entry in the used ring. */
vring_used_ring_id(vq, idx, elem->index);
vring_used_ring_len(vq, idx, len);
uelem.id = elem->index;
uelem.len = len;
vring_used_write(vq, &uelem, idx);
}
void virtqueue_flush(VirtQueue *vq, unsigned int count)