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    SubjectRe: [RFC v3 0/5] virtio: support packed ring
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    On 2018年04月25日 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:
    >
    > https://lkml.org/lkml/2018/4/23/12
    >
    > 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)
    {
           bool avail = flags & cpu_to_vhost16(vq, DESC_AVAIL);

           return avail == vq->avail_wrap_counter;
    }

    So zeroing wrap can not work with this obviously.

    Thanks

    >
    > Some simple functional tests have also been done with
    > Wei's packed ring implementation in QEMU:
    >
    > http://lists.nongnu.org/archive/html/qemu-devel/2018-04/msg00342.html
    >
    > Both of ping and netperf worked as expected (with EVENT_IDX
    > disabled). Reloading the guest driver also worked as expected.
    >
    > TODO:
    > - 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;
    >
    > Thanks!
    >
    > 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(-)
    >

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