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virtio: move allocation to virtqueue_pop/vring_pop

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The return code of virtqueue_pop/vring_pop is unused except to check for
errors or 0.  We can thus easily move allocation inside the functions
and just return a pointer to the VirtQueueElement.

The advantage is that we will be able to allocate only the space that
is needed for the actual size of the s/g list instead of the full
VIRTQUEUE_MAX_SIZE items.  Currently VirtQueueElement takes about 48K
of memory, and this kind of allocation puts a lot of stress on malloc.
By cutting the size by two or three orders of magnitude, malloc can
use much more efficient algorithms.

The patch is pretty large, but changes to each device are testable
more or less independently.  Splitting it would mostly add churn.

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>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
This commit is contained in:
Paolo Bonzini 2016-02-04 16:26:51 +02:00 • committed by Michael S. Tsirkin
parent 6aa46d8ff1
commit 51b19ebe43
22 changed files with 209 additions and 142 deletions
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18
hw/virtio/dataplane/vring.c
View file

@ -389,23 +389,26 @@ static void vring_unmap_element(VirtQueueElement *elem)
*
* Stolen from linux/drivers/vhost/vhost.c.
*/
int vring_pop(VirtIODevice *vdev, Vring *vring,
VirtQueueElement *elem)
void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz)
{
struct vring_desc desc;
unsigned int i, head, found = 0, num = vring->vr.num;
uint16_t avail_idx, last_avail_idx;
VirtQueueElement *elem = NULL;
int ret;
/* Initialize elem so it can be safely unmapped */
elem->in_num = elem->out_num = 0;
/* If there was a fatal error then refuse operation */
if (vring->broken) {
ret = -EFAULT;
goto out;
}
assert(sz >= sizeof(VirtQueueElement));
elem = g_malloc(sz);
/* Initialize elem so it can be safely unmapped */
elem->in_num = elem->out_num = 0;
/* Check it isn't doing very strange things with descriptor numbers. */
last_avail_idx = vring->last_avail_idx;
avail_idx = vring_get_avail_idx(vdev, vring);
@ -481,7 +484,7 @@ int vring_pop(VirtIODevice *vdev, Vring *vring,
virtio_tswap16(vdev, vring->last_avail_idx);
}
return head;
return elem;
out:
assert(ret < 0);
@ -489,7 +492,8 @@ out:
vring->broken = true;
}
vring_unmap_element(elem);
return ret;
g_free(elem);
return NULL;
}
/* After we've used one of their buffers, we tell them about it.