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vring: slim down allocation of VirtQueueElements 

Build the addresses and s/g lists on the stack, and then copy them
to a VirtQueueElement that is just as big as required to contain this
particular s/g list.  The cost of the copy is minimal compared to that
of a large malloc.

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:
Paolo Bonzini 2016-01-31 11:29:02 +01:00 committed by Michael S. Tsirkin
parent 3b3b062821
commit 5dba97ebdc
1 changed files with 35 additions and 16 deletions
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51
hw/virtio/dataplane/vring.c
View File

@ -218,8 +218,14 @@ bool vring_should_notify(VirtIODevice *vdev, Vring *vring)
new, old);
}
typedef struct VirtQueueCurrentElement {
unsigned in_num;
unsigned out_num;
hwaddr addr[VIRTQUEUE_MAX_SIZE];
struct iovec iov[VIRTQUEUE_MAX_SIZE];
} VirtQueueCurrentElement;
static int get_desc(Vring *vring, VirtQueueElement *elem,
static int get_desc(Vring *vring, VirtQueueCurrentElement *elem,
struct vring_desc *desc)
{
unsigned *num;
@ -230,12 +236,12 @@ static int get_desc(Vring *vring, VirtQueueElement *elem,
if (desc->flags & VRING_DESC_F_WRITE) {
num = &elem->in_num;
iov = &elem->in_sg[*num];
addr = &elem->in_addr[*num];
iov = &elem->iov[elem->out_num + *num];
addr = &elem->addr[elem->out_num + *num];
} else {
num = &elem->out_num;
iov = &elem->out_sg[*num];
addr = &elem->out_addr[*num];
iov = &elem->iov[*num];
addr = &elem->addr[*num];
/* If it's an output descriptor, they're all supposed
* to come before any input descriptors. */
@ -299,7 +305,8 @@ static bool read_vring_desc(VirtIODevice *vdev,
/* This is stolen from linux/drivers/vhost/vhost.c. */
static int get_indirect(VirtIODevice *vdev, Vring *vring,
VirtQueueElement *elem, struct vring_desc *indirect)
VirtQueueCurrentElement *cur_elem,
struct vring_desc *indirect)
{
struct vring_desc desc;
unsigned int i = 0, count, found = 0;
@ -351,7 +358,7 @@ static int get_indirect(VirtIODevice *vdev, Vring *vring,
return -EFAULT;
}
ret = get_desc(vring, elem, &desc);
ret = get_desc(vring, cur_elem, &desc);
if (ret < 0) {
vring->broken |= (ret == -EFAULT);
return ret;
@ -394,6 +401,7 @@ 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;
VirtQueueCurrentElement cur_elem;
VirtQueueElement *elem = NULL;
int ret;
@ -403,10 +411,7 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz)
goto out;
}
elem = virtqueue_alloc_element(sz, VIRTQUEUE_MAX_SIZE, VIRTQUEUE_MAX_SIZE);
/* Initialize elem so it can be safely unmapped */
elem->in_num = elem->out_num = 0;
cur_elem.in_num = cur_elem.out_num = 0;
/* Check it isn't doing very strange things with descriptor numbers. */
last_avail_idx = vring->last_avail_idx;
@ -433,8 +438,6 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz)
* the index we've seen. */
head = vring_get_avail_ring(vdev, vring, last_avail_idx % num);
elem->index = head;
/* If their number is silly, that's an error. */
if (unlikely(head >= num)) {
error_report("Guest says index %u > %u is available", head, num);
@ -461,14 +464,14 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz)
barrier();
if (desc.flags & VRING_DESC_F_INDIRECT) {
ret = get_indirect(vdev, vring, elem, &desc);
ret = get_indirect(vdev, vring, &cur_elem, &desc);
if (ret < 0) {
goto out;
}
continue;
}
ret = get_desc(vring, elem, &desc);
ret = get_desc(vring, &cur_elem, &desc);
if (ret < 0) {
goto out;
}
@ -483,6 +486,18 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz)
virtio_tswap16(vdev, vring->last_avail_idx);
}
/* Now copy what we have collected and mapped */
elem = virtqueue_alloc_element(sz, cur_elem.out_num, cur_elem.in_num);
elem->index = head;
for (i = 0; i < cur_elem.out_num; i++) {
elem->out_addr[i] = cur_elem.addr[i];
elem->out_sg[i] = cur_elem.iov[i];
}
for (i = 0; i < cur_elem.in_num; i++) {
elem->in_addr[i] = cur_elem.addr[cur_elem.out_num + i];
elem->in_sg[i] = cur_elem.iov[cur_elem.out_num + i];
}
return elem;
out:
@ -490,7 +505,11 @@ out:
if (ret == -EFAULT) {
vring->broken = true;
}
vring_unmap_element(elem);
for (i = 0; i < cur_elem.out_num + cur_elem.in_num; i++) {
vring_unmap(cur_elem.iov[i].iov_base, false);
}
g_free(elem);
return NULL;
}