[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [RFC v2 5/8] virtio: queue pop for packed ring
From: |
Wei Xu |
Subject: |
Re: [Qemu-devel] [RFC v2 5/8] virtio: queue pop for packed ring |
Date: |
Wed, 6 Jun 2018 11:38:15 +0800 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Wed, Jun 06, 2018 at 11:29:54AM +0800, Jason Wang wrote:
>
>
> On 2018年06月06日 03:08, address@hidden wrote:
> >From: Wei Xu <address@hidden>
> >
> >Signed-off-by: Wei Xu <address@hidden>
> >---
> > hw/virtio/virtio.c | 145
> > ++++++++++++++++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 144 insertions(+), 1 deletion(-)
> >
> >diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> >index cdbb5af..0160d03 100644
> >--- a/hw/virtio/virtio.c
> >+++ b/hw/virtio/virtio.c
> >@@ -1041,7 +1041,7 @@ static void *virtqueue_alloc_element(size_t sz,
> >unsigned out_num, unsigned in_nu
> > return elem;
> > }
> >-void *virtqueue_pop(VirtQueue *vq, size_t sz)
> >+static void *virtqueue_split_pop(VirtQueue *vq, size_t sz)
> > {
> > unsigned int i, head, max;
> > VRingMemoryRegionCaches *caches;
> >@@ -1176,6 +1176,149 @@ err_undo_map:
> > goto done;
> > }
> >+static void *virtqueue_packed_pop(VirtQueue *vq, size_t sz)
> >+{
> >+ unsigned int i, head, max;
> >+ VRingMemoryRegionCaches *caches;
> >+ MemoryRegionCache indirect_desc_cache = MEMORY_REGION_CACHE_INVALID;
> >+ MemoryRegionCache *cache;
> >+ int64_t len;
> >+ VirtIODevice *vdev = vq->vdev;
> >+ VirtQueueElement *elem = NULL;
> >+ unsigned out_num, in_num, elem_entries;
> >+ hwaddr addr[VIRTQUEUE_MAX_SIZE];
> >+ struct iovec iov[VIRTQUEUE_MAX_SIZE];
> >+ VRingDescPacked desc;
> >+
> >+ if (unlikely(vdev->broken)) {
> >+ return NULL;
> >+ }
> >+
> >+ rcu_read_lock();
> >+ if (virtio_queue_packed_empty_rcu(vq)) {
> >+ goto done;
> >+ }
>
> Instead of depending on the barriers inside virtio_queue_packed_empty_rcu().
> I think it's better to keep a smp_rmb() here with comments.
OK.
>
> >+
> >+ /* When we start there are none of either input nor output. */
> >+ out_num = in_num = elem_entries = 0;
> >+
> >+ max = vq->vring.num;
> >+
> >+ if (vq->inuse >= vq->vring.num) {
> >+ virtio_error(vdev, "Virtqueue size exceeded");
> >+ goto done;
> >+ }
> >+
> >+ if (virtio_vdev_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX)) {
> >+ /* FIXME: TBD */
> >+ }
>
> This part could be removed.
My bad, thanks.
>
> >+
> >+ head = vq->last_avail_idx;
> >+ i = head;
> >+
> >+ caches = vring_get_region_caches(vq);
> >+ cache = &caches->desc;
> >+ vring_packed_desc_read(vdev, &desc, cache, i);
>
> I think we'd better find a way to avoid reading descriptor twice.
Do you mean here and the read for empty check?
Wei
>
> Thanks
>
> >+ if (desc.flags & VRING_DESC_F_INDIRECT) {
> >+ if (desc.len % sizeof(VRingDescPacked)) {
> >+ virtio_error(vdev, "Invalid size for indirect buffer table");
> >+ goto done;
> >+ }
> >+
> >+ /* loop over the indirect descriptor table */
> >+ len = address_space_cache_init(&indirect_desc_cache, vdev->dma_as,
> >+ desc.addr, desc.len, false);
> >+ cache = &indirect_desc_cache;
> >+ if (len < desc.len) {
> >+ virtio_error(vdev, "Cannot map indirect buffer");
> >+ goto done;
> >+ }
> >+
> >+ max = desc.len / sizeof(VRingDescPacked);
> >+ i = 0;
> >+ vring_packed_desc_read(vdev, &desc, cache, i);
> >+ }
> >+
> >+ /* Collect all the descriptors */
> >+ while (1) {
> >+ bool map_ok;
> >+
> >+ if (desc.flags & VRING_DESC_F_WRITE) {
> >+ map_ok = virtqueue_map_desc(vdev, &in_num, addr + out_num,
> >+ iov + out_num,
> >+ VIRTQUEUE_MAX_SIZE - out_num, true,
> >+ desc.addr, desc.len);
> >+ } else {
> >+ if (in_num) {
> >+ virtio_error(vdev, "Incorrect order for descriptors");
> >+ goto err_undo_map;
> >+ }
> >+ map_ok = virtqueue_map_desc(vdev, &out_num, addr, iov,
> >+ VIRTQUEUE_MAX_SIZE, false,
> >+ desc.addr, desc.len);
> >+ }
> >+ if (!map_ok) {
> >+ goto err_undo_map;
> >+ }
> >+
> >+ /* If we've got too many, that implies a descriptor loop. */
> >+ if (++elem_entries > max) {
> >+ virtio_error(vdev, "Looped descriptor");
> >+ goto err_undo_map;
> >+ }
> >+
> >+ if (++i >= vq->vring.num) {
> >+ i -= vq->vring.num;
> >+ }
> >+
> >+ if (desc.flags & VRING_DESC_F_NEXT) {
> >+ vring_packed_desc_read(vq->vdev, &desc, cache, i);
> >+ } else {
> >+ break;
> >+ }
> >+ }
> >+
> >+ /* Now copy what we have collected and mapped */
> >+ elem = virtqueue_alloc_element(sz, out_num, in_num);
> >+ for (i = 0; i < out_num; i++) {
> >+ elem->out_addr[i] = addr[i];
> >+ elem->out_sg[i] = iov[i];
> >+ }
> >+ for (i = 0; i < in_num; i++) {
> >+ elem->in_addr[i] = addr[head + out_num + i];
> >+ elem->in_sg[i] = iov[out_num + i];
> >+ }
> >+
> >+ vq->last_avail_idx += (cache == &indirect_desc_cache) ?
> >+ 1 : out_num + in_num;
> >+ if (vq->last_avail_idx >= vq->vring.num) {
> >+ vq->last_avail_idx -= vq->vring.num;
> >+ vq->avail_wrap_counter = !vq->avail_wrap_counter;
> >+ }
> >+ vq->inuse++;
> >+
> >+ trace_virtqueue_pop(vq, elem, elem->in_num, elem->out_num);
> >+done:
> >+ address_space_cache_destroy(&indirect_desc_cache);
> >+ rcu_read_unlock();
> >+
> >+ return elem;
> >+
> >+err_undo_map:
> >+ virtqueue_undo_map_desc(out_num, in_num, iov);
> >+ g_free(elem);
> >+ goto done;
> >+}
> >+
> >+void *virtqueue_pop(VirtQueue *vq, size_t sz)
> >+{
> >+ if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> >+ return virtqueue_packed_pop(vq, sz);
> >+ } else {
> >+ return virtqueue_split_pop(vq, sz);
> >+ }
> >+}
> >+
> > /* virtqueue_drop_all:
> > * @vq: The #VirtQueue
> > * Drops all queued buffers and indicates them to the guest
>
- [Qemu-devel] [RFC v2 2/8] virtio: memory cache for packed ring, (continued)
[Qemu-devel] [RFC v2 6/8] virtio: flush/push for packed ring, wexu, 2018/06/05
[Qemu-devel] [RFC v2 8/8] virtio: guest driver reload for vhost-net, wexu, 2018/06/05
[Qemu-devel] [RFC v2 7/8] virtio: event suppression for packed ring, wexu, 2018/06/05
Re: [Qemu-devel] [RFC v2 0/8] packed ring virtio-net userspace backend support, Jason Wang, 2018/06/05