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Subject: Re: [PATCH net-next v3 00/13] virtio: support packed ring
On Wed, Nov 21, 2018 at 07:20:27AM -0500, Michael S. Tsirkin wrote: > On Wed, Nov 21, 2018 at 06:03:17PM +0800, Tiwei Bie wrote: > > Hi, > > > > This patch set implements packed ring support in virtio driver. > > > > A performance test between pktgen (pktgen_sample03_burst_single_flow.sh) > > and DPDK vhost (testpmd/rxonly/vhost-PMD) has been done, I saw > > ~30% performance gain in packed ring in this case. > > Thanks a lot, this is very exciting! > Dave, given the holiday, attempts to wrap up the 1.1 spec and the > patchset size I would very much appreciate a bit more time for > review. Say until Nov 28? > > > 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): > > > > https://lkml.org/lkml/2018/7/3/33 > > Could you pls clarify - do you mean it doesn't yet work with vhost > because of a vhost bug, and to test it with the linked patches > you had to hack in _F_NEXT? Because I do not see _F_NEXT > in indirect descriptors in this patch (which is fine). > Or did I miss it? You didn't miss anything. :) I think it's a small bug in vhost, which Jason may fix very quickly, so I didn't post it. Below is the hack I used: diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index cd7e755484e3..42faea7d8cf8 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -980,6 +980,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq, unsigned int i, n, err_idx; u16 head, id; dma_addr_t addr; + int c = 0; head = vq->packed.next_avail_idx; desc = alloc_indirect_packed(total_sg, gfp); @@ -1001,8 +1002,9 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq, if (vring_mapping_error(vq, addr)) goto unmap_release; - desc[i].flags = cpu_to_le16(n < out_sgs ? - 0 : VRING_DESC_F_WRITE); + desc[i].flags = cpu_to_le16((n < out_sgs ? + 0 : VRING_DESC_F_WRITE) | + (++c == total_sg ? 0 : VRING_DESC_F_NEXT)); desc[i].addr = cpu_to_le64(addr); desc[i].len = cpu_to_le32(sg->length); i++; -- 2.14.1 > > > 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(-) > > > > -- > > 2.14.5
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