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>
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3b3b062821
commit
5dba97ebdc
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@ -218,8 +218,14 @@ bool vring_should_notify(VirtIODevice *vdev, Vring *vring)
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new, old);
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new, old);
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}
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}
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typedef struct VirtQueueCurrentElement {
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unsigned in_num;
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unsigned out_num;
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hwaddr addr[VIRTQUEUE_MAX_SIZE];
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struct iovec iov[VIRTQUEUE_MAX_SIZE];
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} VirtQueueCurrentElement;
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static int get_desc(Vring *vring, VirtQueueElement *elem,
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static int get_desc(Vring *vring, VirtQueueCurrentElement *elem,
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struct vring_desc *desc)
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struct vring_desc *desc)
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{
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{
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unsigned *num;
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unsigned *num;
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@ -230,12 +236,12 @@ static int get_desc(Vring *vring, VirtQueueElement *elem,
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if (desc->flags & VRING_DESC_F_WRITE) {
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if (desc->flags & VRING_DESC_F_WRITE) {
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num = &elem->in_num;
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num = &elem->in_num;
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iov = &elem->in_sg[*num];
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iov = &elem->iov[elem->out_num + *num];
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addr = &elem->in_addr[*num];
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addr = &elem->addr[elem->out_num + *num];
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} else {
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} else {
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num = &elem->out_num;
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num = &elem->out_num;
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iov = &elem->out_sg[*num];
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iov = &elem->iov[*num];
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addr = &elem->out_addr[*num];
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addr = &elem->addr[*num];
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/* If it's an output descriptor, they're all supposed
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/* If it's an output descriptor, they're all supposed
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* to come before any input descriptors. */
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* to come before any input descriptors. */
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@ -299,7 +305,8 @@ static bool read_vring_desc(VirtIODevice *vdev,
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/* This is stolen from linux/drivers/vhost/vhost.c. */
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/* This is stolen from linux/drivers/vhost/vhost.c. */
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static int get_indirect(VirtIODevice *vdev, Vring *vring,
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static int get_indirect(VirtIODevice *vdev, Vring *vring,
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VirtQueueElement *elem, struct vring_desc *indirect)
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VirtQueueCurrentElement *cur_elem,
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struct vring_desc *indirect)
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{
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{
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struct vring_desc desc;
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struct vring_desc desc;
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unsigned int i = 0, count, found = 0;
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unsigned int i = 0, count, found = 0;
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@ -351,7 +358,7 @@ static int get_indirect(VirtIODevice *vdev, Vring *vring,
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return -EFAULT;
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return -EFAULT;
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}
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}
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ret = get_desc(vring, elem, &desc);
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ret = get_desc(vring, cur_elem, &desc);
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if (ret < 0) {
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if (ret < 0) {
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vring->broken |= (ret == -EFAULT);
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vring->broken |= (ret == -EFAULT);
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return ret;
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return ret;
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@ -394,6 +401,7 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz)
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struct vring_desc desc;
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struct vring_desc desc;
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unsigned int i, head, found = 0, num = vring->vr.num;
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unsigned int i, head, found = 0, num = vring->vr.num;
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uint16_t avail_idx, last_avail_idx;
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uint16_t avail_idx, last_avail_idx;
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VirtQueueCurrentElement cur_elem;
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VirtQueueElement *elem = NULL;
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VirtQueueElement *elem = NULL;
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int ret;
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int ret;
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@ -403,10 +411,7 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz)
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goto out;
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goto out;
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}
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}
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elem = virtqueue_alloc_element(sz, VIRTQUEUE_MAX_SIZE, VIRTQUEUE_MAX_SIZE);
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cur_elem.in_num = cur_elem.out_num = 0;
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/* Initialize elem so it can be safely unmapped */
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elem->in_num = elem->out_num = 0;
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/* Check it isn't doing very strange things with descriptor numbers. */
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/* Check it isn't doing very strange things with descriptor numbers. */
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last_avail_idx = vring->last_avail_idx;
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last_avail_idx = vring->last_avail_idx;
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@ -433,8 +438,6 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz)
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* the index we've seen. */
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* the index we've seen. */
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head = vring_get_avail_ring(vdev, vring, last_avail_idx % num);
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head = vring_get_avail_ring(vdev, vring, last_avail_idx % num);
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elem->index = head;
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/* If their number is silly, that's an error. */
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/* If their number is silly, that's an error. */
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if (unlikely(head >= num)) {
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if (unlikely(head >= num)) {
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error_report("Guest says index %u > %u is available", head, num);
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error_report("Guest says index %u > %u is available", head, num);
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@ -461,14 +464,14 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz)
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barrier();
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barrier();
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if (desc.flags & VRING_DESC_F_INDIRECT) {
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if (desc.flags & VRING_DESC_F_INDIRECT) {
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ret = get_indirect(vdev, vring, elem, &desc);
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ret = get_indirect(vdev, vring, &cur_elem, &desc);
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if (ret < 0) {
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if (ret < 0) {
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goto out;
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goto out;
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}
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}
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continue;
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continue;
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}
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}
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ret = get_desc(vring, elem, &desc);
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ret = get_desc(vring, &cur_elem, &desc);
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if (ret < 0) {
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if (ret < 0) {
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goto out;
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goto out;
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}
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}
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@ -483,6 +486,18 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz)
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virtio_tswap16(vdev, vring->last_avail_idx);
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virtio_tswap16(vdev, vring->last_avail_idx);
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}
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}
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/* Now copy what we have collected and mapped */
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elem = virtqueue_alloc_element(sz, cur_elem.out_num, cur_elem.in_num);
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elem->index = head;
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for (i = 0; i < cur_elem.out_num; i++) {
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elem->out_addr[i] = cur_elem.addr[i];
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elem->out_sg[i] = cur_elem.iov[i];
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}
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for (i = 0; i < cur_elem.in_num; i++) {
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elem->in_addr[i] = cur_elem.addr[cur_elem.out_num + i];
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elem->in_sg[i] = cur_elem.iov[cur_elem.out_num + i];
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}
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return elem;
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return elem;
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out:
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out:
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@ -490,7 +505,11 @@ out:
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if (ret == -EFAULT) {
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if (ret == -EFAULT) {
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vring->broken = true;
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vring->broken = true;
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}
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}
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vring_unmap_element(elem);
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for (i = 0; i < cur_elem.out_num + cur_elem.in_num; i++) {
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vring_unmap(cur_elem.iov[i].iov_base, false);
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}
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g_free(elem);
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g_free(elem);
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return NULL;
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return NULL;
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}
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}
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