virtio: move allocation to virtqueue_pop/vring_pop

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>

1 files changed, 43 insertions, 26 deletions

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index fde8dd3..de696e8 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -819,20 +819,24 @@ static void virtio_net_handle_ctrl(VirtIODevice *vdev, VirtQueue *vq)
     VirtIONet *n = VIRTIO_NET(vdev);
     struct virtio_net_ctrl_hdr ctrl;
     virtio_net_ctrl_ack status = VIRTIO_NET_ERR;
-    VirtQueueElement elem;
+    VirtQueueElement *elem;
     size_t s;
     struct iovec *iov, *iov2;
     unsigned int iov_cnt;
 
-    while (virtqueue_pop(vq, &elem)) {
-        if (iov_size(elem.in_sg, elem.in_num) < sizeof(status) ||
-            iov_size(elem.out_sg, elem.out_num) < sizeof(ctrl)) {
+    for (;;) {
+        elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+        if (!elem) {
+            break;
+        }
+        if (iov_size(elem->in_sg, elem->in_num) < sizeof(status) ||
+            iov_size(elem->out_sg, elem->out_num) < sizeof(ctrl)) {
             error_report("virtio-net ctrl missing headers");
             exit(1);
         }
 
-        iov_cnt = elem.out_num;
-        iov2 = iov = g_memdup(elem.out_sg, sizeof(struct iovec) * elem.out_num);
+        iov_cnt = elem->out_num;
+        iov2 = iov = g_memdup(elem->out_sg, sizeof(struct iovec) * elem->out_num);
         s = iov_to_buf(iov, iov_cnt, 0, &ctrl, sizeof(ctrl));
         iov_discard_front(&iov, &iov_cnt, sizeof(ctrl));
         if (s != sizeof(ctrl)) {
@@ -851,12 +855,13 @@ static void virtio_net_handle_ctrl(VirtIODevice *vdev, VirtQueue *vq)
             status = virtio_net_handle_offloads(n, ctrl.cmd, iov, iov_cnt);
         }
 
-        s = iov_from_buf(elem.in_sg, elem.in_num, 0, &status, sizeof(status));
+        s = iov_from_buf(elem->in_sg, elem->in_num, 0, &status, sizeof(status));
         assert(s == sizeof(status));
 
-        virtqueue_push(vq, &elem, sizeof(status));
+        virtqueue_push(vq, elem, sizeof(status));
         virtio_notify(vdev, vq);
         g_free(iov2);
+        g_free(elem);
     }
 }
 
@@ -1045,13 +1050,14 @@ static ssize_t virtio_net_receive(NetClientState *nc, const uint8_t *buf, size_t
     offset = i = 0;
 
     while (offset < size) {
-        VirtQueueElement elem;
+        VirtQueueElement *elem;
         int len, total;
-        const struct iovec *sg = elem.in_sg;
+        const struct iovec *sg;
 
         total = 0;
 
-        if (virtqueue_pop(q->rx_vq, &elem) == 0) {
+        elem = virtqueue_pop(q->rx_vq, sizeof(VirtQueueElement));
+        if (!elem) {
             if (i == 0)
                 return -1;
             error_report("virtio-net unexpected empty queue: "
@@ -1064,21 +1070,22 @@ static ssize_t virtio_net_receive(NetClientState *nc, const uint8_t *buf, size_t
             exit(1);
         }
 
-        if (elem.in_num < 1) {
+        if (elem->in_num < 1) {
             error_report("virtio-net receive queue contains no in buffers");
             exit(1);
         }
 
+        sg = elem->in_sg;
         if (i == 0) {
             assert(offset == 0);
             if (n->mergeable_rx_bufs) {
                 mhdr_cnt = iov_copy(mhdr_sg, ARRAY_SIZE(mhdr_sg),
-                                    sg, elem.in_num,
+                                    sg, elem->in_num,
                                     offsetof(typeof(mhdr), num_buffers),
                                     sizeof(mhdr.num_buffers));
             }
 
-            receive_header(n, sg, elem.in_num, buf, size);
+            receive_header(n, sg, elem->in_num, buf, size);
             offset = n->host_hdr_len;
             total += n->guest_hdr_len;
             guest_offset = n->guest_hdr_len;
@@ -1087,7 +1094,7 @@ static ssize_t virtio_net_receive(NetClientState *nc, const uint8_t *buf, size_t
         }
 
         /* copy in packet.  ugh */
-        len = iov_from_buf(sg, elem.in_num, guest_offset,
+        len = iov_from_buf(sg, elem->in_num, guest_offset,
                            buf + offset, size - offset);
         total += len;
         offset += len;
@@ -1095,12 +1102,14 @@ static ssize_t virtio_net_receive(NetClientState *nc, const uint8_t *buf, size_t
          * must have consumed the complete packet.
          * Otherwise, drop it. */
         if (!n->mergeable_rx_bufs && offset < size) {
-            virtqueue_discard(q->rx_vq, &elem, total);
+            virtqueue_discard(q->rx_vq, elem, total);
+            g_free(elem);
             return size;
         }
 
         /* signal other side */
-        virtqueue_fill(q->rx_vq, &elem, total, i++);
+        virtqueue_fill(q->rx_vq, elem, total, i++);
+        g_free(elem);
     }
 
     if (mhdr_cnt) {
@@ -1124,10 +1133,11 @@ static void virtio_net_tx_complete(NetClientState *nc, ssize_t len)
     VirtIONetQueue *q = virtio_net_get_subqueue(nc);
     VirtIODevice *vdev = VIRTIO_DEVICE(n);
 
-    virtqueue_push(q->tx_vq, &q->async_tx.elem, 0);
+    virtqueue_push(q->tx_vq, q->async_tx.elem, 0);
     virtio_notify(vdev, q->tx_vq);
 
-    q->async_tx.elem.out_num = 0;
+    g_free(q->async_tx.elem);
+    q->async_tx.elem = NULL;
 
     virtio_queue_set_notification(q->tx_vq, 1);
     virtio_net_flush_tx(q);
@@ -1138,25 +1148,31 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
 {
     VirtIONet *n = q->n;
     VirtIODevice *vdev = VIRTIO_DEVICE(n);
-    VirtQueueElement elem;
+    VirtQueueElement *elem;
     int32_t num_packets = 0;
     int queue_index = vq2q(virtio_get_queue_index(q->tx_vq));
     if (!(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
         return num_packets;
     }
 
-    if (q->async_tx.elem.out_num) {
+    if (q->async_tx.elem) {
         virtio_queue_set_notification(q->tx_vq, 0);
         return num_packets;
     }
 
-    while (virtqueue_pop(q->tx_vq, &elem)) {
+    for (;;) {
         ssize_t ret;
-        unsigned int out_num = elem.out_num;
-        struct iovec *out_sg = &elem.out_sg[0];
-        struct iovec sg[VIRTQUEUE_MAX_SIZE], sg2[VIRTQUEUE_MAX_SIZE + 1];
+        unsigned int out_num;
+        struct iovec sg[VIRTQUEUE_MAX_SIZE], sg2[VIRTQUEUE_MAX_SIZE + 1], *out_sg;
         struct virtio_net_hdr_mrg_rxbuf mhdr;
 
+        elem = virtqueue_pop(q->tx_vq, sizeof(VirtQueueElement));
+        if (!elem) {
+            break;
+        }
+
+        out_num = elem->out_num;
+        out_sg = elem->out_sg;
         if (out_num < 1) {
             error_report("virtio-net header not in first element");
             exit(1);
@@ -1208,8 +1224,9 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
         }
 
 drop:
-        virtqueue_push(q->tx_vq, &elem, 0);
+        virtqueue_push(q->tx_vq, elem, 0);
         virtio_notify(vdev, q->tx_vq);
+        g_free(elem);
 
         if (++num_packets >= n->tx_burst) {
             break;