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, 50 insertions, 30 deletions

diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
index 8d5c740..cf3d12b 100644
--- a/hw/char/virtio-serial-bus.c
+++ b/hw/char/virtio-serial-bus.c
@@ -83,7 +83,7 @@ static bool use_multiport(VirtIOSerial *vser)
 static size_t write_to_port(VirtIOSerialPort *port,
                             const uint8_t *buf, size_t size)
 {
-    VirtQueueElement elem;
+    VirtQueueElement *elem;
     VirtQueue *vq;
     size_t offset;
 
@@ -96,15 +96,17 @@ static size_t write_to_port(VirtIOSerialPort *port,
     while (offset < size) {
         size_t len;
 
-        if (!virtqueue_pop(vq, &elem)) {
+        elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+        if (!elem) {
             break;
         }
 
-        len = iov_from_buf(elem.in_sg, elem.in_num, 0,
+        len = iov_from_buf(elem->in_sg, elem->in_num, 0,
                            buf + offset, size - offset);
         offset += len;
 
-        virtqueue_push(vq, &elem, len);
+        virtqueue_push(vq, elem, len);
+        g_free(elem);
     }
 
     virtio_notify(VIRTIO_DEVICE(port->vser), vq);
@@ -113,13 +115,18 @@ static size_t write_to_port(VirtIOSerialPort *port,
 
 static void discard_vq_data(VirtQueue *vq, VirtIODevice *vdev)
 {
-    VirtQueueElement elem;
+    VirtQueueElement *elem;
 
     if (!virtio_queue_ready(vq)) {
         return;
     }
-    while (virtqueue_pop(vq, &elem)) {
-        virtqueue_push(vq, &elem, 0);
+    for (;;) {
+        elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+        if (!elem) {
+            break;
+        }
+        virtqueue_push(vq, elem, 0);
+        g_free(elem);
     }
     virtio_notify(vdev, vq);
 }
@@ -138,21 +145,22 @@ static void do_flush_queued_data(VirtIOSerialPort *port, VirtQueue *vq,
         unsigned int i;
 
         /* Pop an elem only if we haven't left off a previous one mid-way */
-        if (!port->elem.out_num) {
-            if (!virtqueue_pop(vq, &port->elem)) {
+        if (!port->elem) {
+            port->elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+            if (!port->elem) {
                 break;
             }
             port->iov_idx = 0;
             port->iov_offset = 0;
         }
 
-        for (i = port->iov_idx; i < port->elem.out_num; i++) {
+        for (i = port->iov_idx; i < port->elem->out_num; i++) {
             size_t buf_size;
             ssize_t ret;
 
-            buf_size = port->elem.out_sg[i].iov_len - port->iov_offset;
+            buf_size = port->elem->out_sg[i].iov_len - port->iov_offset;
             ret = vsc->have_data(port,
-                                  port->elem.out_sg[i].iov_base
+                                  port->elem->out_sg[i].iov_base
                                   + port->iov_offset,
                                   buf_size);
             if (port->throttled) {
@@ -167,8 +175,9 @@ static void do_flush_queued_data(VirtIOSerialPort *port, VirtQueue *vq,
         if (port->throttled) {
             break;
         }
-        virtqueue_push(vq, &port->elem, 0);
-        port->elem.out_num = 0;
+        virtqueue_push(vq, port->elem, 0);
+        g_free(port->elem);
+        port->elem = NULL;
     }
     virtio_notify(vdev, vq);
 }
@@ -185,22 +194,26 @@ static void flush_queued_data(VirtIOSerialPort *port)
 
 static size_t send_control_msg(VirtIOSerial *vser, void *buf, size_t len)
 {
-    VirtQueueElement elem;
+    VirtQueueElement *elem;
     VirtQueue *vq;
 
     vq = vser->c_ivq;
     if (!virtio_queue_ready(vq)) {
         return 0;
     }
-    if (!virtqueue_pop(vq, &elem)) {
+
+    elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+    if (!elem) {
         return 0;
     }
 
     /* TODO: detect a buffer that's too short, set NEEDS_RESET */
-    iov_from_buf(elem.in_sg, elem.in_num, 0, buf, len);
+    iov_from_buf(elem->in_sg, elem->in_num, 0, buf, len);
 
-    virtqueue_push(vq, &elem, len);
+    virtqueue_push(vq, elem, len);
     virtio_notify(VIRTIO_DEVICE(vser), vq);
+    g_free(elem);
+
     return len;
 }
 
@@ -414,7 +427,7 @@ static void control_in(VirtIODevice *vdev, VirtQueue *vq)
 
 static void control_out(VirtIODevice *vdev, VirtQueue *vq)
 {
-    VirtQueueElement elem;
+    VirtQueueElement *elem;
     VirtIOSerial *vser;
     uint8_t *buf;
     size_t len;
@@ -423,10 +436,15 @@ static void control_out(VirtIODevice *vdev, VirtQueue *vq)
 
     len = 0;
     buf = NULL;
-    while (virtqueue_pop(vq, &elem)) {
+    for (;;) {
         size_t cur_len;
 
-        cur_len = iov_size(elem.out_sg, elem.out_num);
+        elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+        if (!elem) {
+            break;
+        }
+
+        cur_len = iov_size(elem->out_sg, elem->out_num);
         /*
          * Allocate a new buf only if we didn't have one previously or
          * if the size of the buf differs
@@ -437,10 +455,11 @@ static void control_out(VirtIODevice *vdev, VirtQueue *vq)
             buf = g_malloc(cur_len);
             len = cur_len;
         }
-        iov_to_buf(elem.out_sg, elem.out_num, 0, buf, cur_len);
+        iov_to_buf(elem->out_sg, elem->out_num, 0, buf, cur_len);
 
         handle_control_message(vser, buf, cur_len);
-        virtqueue_push(vq, &elem, 0);
+        virtqueue_push(vq, elem, 0);
+        g_free(elem);
     }
     g_free(buf);
     virtio_notify(vdev, vq);
@@ -620,7 +639,7 @@ static void virtio_serial_save_device(VirtIODevice *vdev, QEMUFile *f)
         qemu_put_byte(f, port->host_connected);
 
 	elem_popped = 0;
-        if (port->elem.out_num) {
+        if (port->elem) {
             elem_popped = 1;
         }
         qemu_put_be32s(f, &elem_popped);
@@ -628,8 +647,8 @@ static void virtio_serial_save_device(VirtIODevice *vdev, QEMUFile *f)
             qemu_put_be32s(f, &port->iov_idx);
             qemu_put_be64s(f, &port->iov_offset);
 
-            qemu_put_buffer(f, (unsigned char *)&port->elem,
-                            sizeof(port->elem));
+            qemu_put_buffer(f, (unsigned char *)port->elem,
+                            sizeof(VirtQueueElement));
         }
     }
 }
@@ -704,9 +723,10 @@ static int fetch_active_ports_list(QEMUFile *f, int version_id,
                 qemu_get_be32s(f, &port->iov_idx);
                 qemu_get_be64s(f, &port->iov_offset);
 
-                qemu_get_buffer(f, (unsigned char *)&port->elem,
-                                sizeof(port->elem));
-                virtqueue_map(&port->elem);
+                port->elem = g_new(VirtQueueElement, 1);
+                qemu_get_buffer(f, (unsigned char *)port->elem,
+                                sizeof(VirtQueueElement));
+                virtqueue_map(port->elem);
 
                 /*
                  *  Port was throttled on source machine.  Let's
@@ -928,7 +948,7 @@ static void virtser_port_device_realize(DeviceState *dev, Error **errp)
         return;
     }
 
-    port->elem.out_num = 0;
+    port->elem = NULL;
 }
 
 static void virtser_port_device_plug(HotplugHandler *hotplug_dev,