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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
Download patch file Download diff file Expand all files Collapse all files

11
hw/block/dataplane/virtio-blk.c
View file

@ -100,20 +100,19 @@ static void handle_notify(EventNotifier *e)
blk_io_plug(s->conf->conf.blk);
for (;;) {
MultiReqBuffer mrb = {};
int ret;
/* Disable guest->host notifies to avoid unnecessary vmexits */
vring_disable_notification(s->vdev, &s->vring);
for (;;) {
VirtIOBlockReq *req = virtio_blk_alloc_request(vblk);
VirtIOBlockReq *req = vring_pop(s->vdev, &s->vring,
sizeof(VirtIOBlockReq));
ret = vring_pop(s->vdev, &s->vring, &req->elem);
if (ret < 0) {
virtio_blk_free_request(req);
if (req == NULL) {
break; /* no more requests */
}
virtio_blk_init_request(vblk, req);
trace_virtio_blk_data_plane_process_request(s, req->elem.out_num,
req->elem.in_num,
req->elem.index);
@ -125,7 +124,7 @@ static void handle_notify(EventNotifier *e)
virtio_blk_submit_multireq(s->conf->conf.blk, &mrb);
}
if (likely(ret == -EAGAIN)) { /* vring emptied */
if (likely(!vring_more_avail(s->vdev, &s->vring))) { /* vring emptied */
/* Re-enable guest->host notifies and stop processing the vring.
* But if the guest has snuck in more descriptors, keep processing.
*/

15
hw/block/virtio-blk.c
View file

@ -29,15 +29,13 @@
#include "hw/virtio/virtio-bus.h"
#include "hw/virtio/virtio-access.h"
VirtIOBlockReq *virtio_blk_alloc_request(VirtIOBlock *s)
void virtio_blk_init_request(VirtIOBlock *s, VirtIOBlockReq *req)
{
VirtIOBlockReq *req = g_new(VirtIOBlockReq, 1);
req->dev = s;
req->qiov.size = 0;
req->in_len = 0;
req->next = NULL;
req->mr_next = NULL;
return req;
}
void virtio_blk_free_request(VirtIOBlockReq *req)
@ -193,13 +191,11 @@ out:
static VirtIOBlockReq *virtio_blk_get_request(VirtIOBlock *s)
{
VirtIOBlockReq *req = virtio_blk_alloc_request(s);
VirtIOBlockReq *req = virtqueue_pop(s->vq, sizeof(VirtIOBlockReq));
if (!virtqueue_pop(s->vq, &req->elem)) {
virtio_blk_free_request(req);
return NULL;
if (req) {
virtio_blk_init_request(s, req);
}
return req;
}
@ -836,7 +832,8 @@ static int virtio_blk_load_device(VirtIODevice *vdev, QEMUFile *f,
VirtIOBlock *s = VIRTIO_BLK(vdev);
while (qemu_get_sbyte(f)) {
VirtIOBlockReq *req = virtio_blk_alloc_request(s);
VirtIOBlockReq *req = g_new(VirtIOBlockReq, 1);
virtio_blk_init_request(s, req);
qemu_get_buffer(f, (unsigned char *)&req->elem,
sizeof(VirtQueueElement));
req->next = s->rq;