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Subject[PATCH net-next v3 00/13] virtio: support packed ring

This patch set implements packed ring support in virtio driver.

A performance test between pktgen (
and DPDK vhost (testpmd/rxonly/vhost-PMD) has been done, I saw
~30% performance gain in packed ring in this case.

To make this patch set work with below patch set for vhost,
some hacks are needed to set the _F_NEXT flag in indirect
descriptors (this should be fixed in vhost):

v2 -> v3:
- Use leXX instead of virtioXX (MST);
- Refactor split ring first (MST);
- Add debug helpers (MST);
- Put split/packed ring specific fields in sub structures (MST);
- Handle normal descriptors and indirect descriptors differently (MST);
- Track the DMA addr/len related info in a separate structure (MST);
- Calculate AVAIL/USED flags only when wrap counter wraps (MST);
- Define a struct/union to read event structure (MST);
- Define a macro for wrap counter bit in uapi (MST);
- Define the AVAIL/USED bits as shifts instead of values (MST);
- s/_F_/_FLAG_/ in VRING_PACKED_EVENT_* as they are values (MST);
- Drop the notify workaround for QEMU's tx-timer in packed ring (MST);

v1 -> v2:
- Use READ_ONCE() to read event off_wrap and flags together (Jason);
- Add comments related to ccw (Jason);

RFC v6 -> v1:
- Avoid extra virtio_wmb() in virtqueue_enable_cb_delayed_packed()
when event idx is off (Jason);
- Fix bufs calculation in virtqueue_enable_cb_delayed_packed() (Jason);
- Test the state of the desc at used_idx instead of last_used_idx
in virtqueue_enable_cb_delayed_packed() (Jason);
- Save wrap counter (as part of queue state) in the return value
of virtqueue_enable_cb_prepare_packed();
- Refine the packed ring definitions in uapi;
- Rebase on the net-next tree;

RFC v5 -> RFC v6:
- Avoid tracking addr/len/flags when DMA API isn't used (MST/Jason);
- Define wrap counter as bool (Jason);
- Use ALIGN() in vring_init_packed() (Jason);
- Avoid using pointer to track `next` in detach_buf_packed() (Jason);
- Add comments for barriers (Jason);
- Don't enable RING_PACKED on ccw for now (noticed by Jason);
- Refine the memory barrier in virtqueue_poll();
- Add a missing memory barrier in virtqueue_enable_cb_delayed_packed();
- Remove the hacks in virtqueue_enable_cb_prepare_packed();

RFC v4 -> RFC v5:
- Save DMA addr, etc in desc state (Jason);
- Track used wrap counter;

RFC v3 -> RFC v4:
- Make ID allocation support out-of-order (Jason);
- Various fixes for EVENT_IDX support;

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 (13):
virtio: add packed ring types and macros
virtio_ring: add _split suffix for split ring functions
virtio_ring: put split ring functions together
virtio_ring: put split ring fields in a sub struct
virtio_ring: introduce debug helpers
virtio_ring: introduce helper for indirect feature
virtio_ring: allocate desc state for split ring separately
virtio_ring: extract split ring handling from ring creation
virtio_ring: cache whether we will use DMA API
virtio_ring: introduce packed ring support
virtio_ring: leverage event idx in packed ring
virtio_ring: disable packed ring on unsupported transports
virtio_ring: advertize packed ring layout

drivers/misc/mic/vop/vop_main.c | 13 +
drivers/remoteproc/remoteproc_virtio.c | 13 +
drivers/s390/virtio/virtio_ccw.c | 14 +
drivers/virtio/virtio_ring.c | 1811 +++++++++++++++++++++++++-------
include/uapi/linux/virtio_config.h | 3 +
include/uapi/linux/virtio_ring.h | 52 +
6 files changed, 1530 insertions(+), 376 deletions(-)


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