Re: [RFC v3 0/5] virtio: support packed ring

From: Jason Wang
Date: Thu Apr 26 2018 - 23:56:28 EST

On 2018å04æ25æ 13:15, Tiwei Bie wrote:
Hello everyone,

This RFC implements packed ring support in virtio driver.

Some simple functional tests have been done with Jason's
packed ring implementation in vhost:

Both of ping and netperf worked as expected (with EVENT_IDX
disabled). But there are below known issues:

1. Reloading the guest driver will break the Tx/Rx;

Will have a look at this issue.

2. Zeroing the flags when detaching a used desc will
break the guest -> host path.

I still think zeroing flags is unnecessary or even a bug. At host, I track last observed avail wrap counter and detect avail like (what is suggested in the example code in the spec):

static bool desc_is_avail(struct vhost_virtqueue *vq, __virtio16 flags)
ÂÂÂÂÂÂ bool avail = flags & cpu_to_vhost16(vq, DESC_AVAIL);

ÂÂÂÂÂÂ return avail == vq->avail_wrap_counter;

So zeroing wrap can not work with this obviously.


Some simple functional tests have also been done with
Wei's packed ring implementation in QEMU:

Both of ping and netperf worked as expected (with EVENT_IDX
disabled). Reloading the guest driver also worked as expected.

- Refinements (for code and commit log) and bug fixes;
- Discuss/fix/test EVENT_IDX support;
- Test devices other than net;

RFC v2 -> RFC v3:
- Split into small patches (Jason);
- Add helper virtqueue_use_indirect() (Jason);
- Just set id for the last descriptor of a list (Jason);
- Calculate the prev in virtqueue_add_packed() (Jason);
- Fix/improve desc suppression code (Jason/MST);
- Refine the code layout for XXX_split/packed and wrappers (MST);
- Fix the comments and API in uapi (MST);
- Remove the BUG_ON() for indirect (Jason);
- Some other refinements and bug fixes;

RFC v1 -> RFC v2:
- Add indirect descriptor support - compile test only;
- Add event suppression supprt - compile test only;
- Move vring_packed_init() out of uapi (Jason, MST);
- Merge two loops into one in virtqueue_add_packed() (Jason);
- Split vring_unmap_one() for packed ring and split ring (Jason);
- Avoid using '%' operator (Jason);
- Rename free_head -> next_avail_idx (Jason);
- Add comments for virtio_wmb() in virtqueue_add_packed() (Jason);
- Some other refinements and bug fixes;


Tiwei Bie (5):
virtio: add packed ring definitions
virtio_ring: support creating packed ring
virtio_ring: add packed ring support
virtio_ring: add event idx support in packed ring
virtio_ring: enable packed ring

drivers/virtio/virtio_ring.c | 1271 ++++++++++++++++++++++++++++--------
include/linux/virtio_ring.h | 8 +-
include/uapi/linux/virtio_config.h | 12 +-
include/uapi/linux/virtio_ring.h | 36 +
4 files changed, 1049 insertions(+), 278 deletions(-)