On Mon, Sep 10, 2018 at 11:33:17AM +0800, Jason Wang wrote: > On 2018年09月10日 11:00, Tiwei Bie wrote: > > On Fri, Sep 07, 2018 at 09:00:49AM -0400, Michael S. Tsirkin wrote: > > > On Fri, Sep 07, 2018 at 09:22:25AM +0800, Tiwei Bie wrote: > > > > On Mon, Aug 27, 2018 at 05:00:40PM +0300, Michael S. Tsirkin wrote: > > > > > Are there still plans to test the performance with vost pmd? > > > > > vhost doesn't seem to show a performance gain ... > > > > > > > > > I tried some performance tests with vhost PMD. In guest, the > > > > XDP program will return XDP_DROP directly. And in host, testpmd > > > > will do txonly fwd. > > > > > > > > When burst size is 1 and packet size is 64 in testpmd and > > > > testpmd needs to iterate 5 Tx queues (but only the first two > > > > queues are enabled) to prepare and inject packets, I got ~12% > > > > performance boost (5.7Mpps -> 6.4Mpps). And if the vhost PMD > > > > is faster (e.g. just need to iterate the first two queues to > > > > prepare and inject packets), then I got similar performance > > > > for both rings (~9.9Mpps) (packed ring's performance can be > > > > lower, because it's more complicated in driver.) > > > > > > > > I think packed ring makes vhost PMD faster, but it doesn't make > > > > the driver faster. In packed ring, the ring is simplified, and > > > > the handling of the ring in vhost (device) is also simplified, > > > > but things are not simplified in driver, e.g. although there is > > > > no desc table in the virtqueue anymore, driver still needs to > > > > maintain a private desc state table (which is still managed as > > > > a list in this patch set) to support the out-of-order desc > > > > processing in vhost (device). > > > > > > > > I think this patch set is mainly to make the driver have a full > > > > functional support for the packed ring, which makes it possible > > > > to leverage the packed ring feature in vhost (device). But I'm > > > > not sure whether there is any other better idea, I'd like to > > > > hear your thoughts. Thanks! > > > Just this: Jens seems to report a nice gain with virtio and > > > vhost pmd across the board. Try to compare virtio and > > > virtio pmd to see what does pmd do better? > > The virtio PMD (drivers/net/virtio) in DPDK doesn't need to share > > the virtio ring operation code with other drivers and is highly > > optimized for network. E.g. in Rx, the Rx burst function won't > > chain descs. So the ID management for the Rx ring can be quite > > simple and straightforward, we just need to initialize these IDs > > when initializing the ring and don't need to change these IDs > > in data path anymore (the mergable Rx code in that patch set > > assumes the descs will be written back in order, which should be > > fixed. I.e., the ID in the desc should be used to index vq->descx[]). > > The Tx code in that patch set also assumes the descs will be > > written back by device in order, which should be fixed. > > Yes it is. I think I've pointed it out in some early version of pmd patch. > So I suspect part (or all) of the boost may come from in order feature. > > > > > But in kernel virtio driver, the virtio_ring.c is very generic. > > The enqueue (virtqueue_add()) and dequeue (virtqueue_get_buf_ctx()) > > functions need to support all the virtio devices and should be > > able to handle all the possible cases that may happen. So although > > the packed ring can be very efficient in some cases, currently > > the room to optimize the performance in kernel's virtio_ring.c > > isn't that much. If we want to take the fully advantage of the > > packed ring's efficiency, we need some further e.g. API changes > > in virtio_ring.c, which shouldn't be part of this patch set. > > Could you please share more thoughts on this e.g how to improve the API? > Notice since the API is shared by both split ring and packed ring, it may > improve the performance of split ring as well. One can easily imagine a > batching API, but it does not have many real users now, the only case is the > XDP transmission which can accept an array of XDP frames. I don't have detailed thoughts on this yet. But kernel's virtio_ring.c is quite generic compared with what we did in virtio PMD. > > > So > > I still think this patch set is mainly to make the kernel virtio > > driver to have a full functional support of the packed ring, and > > we can't expect impressive performance boost with it. > > We can only gain when virtio ring layout is the bottleneck. If there're > bottlenecks elsewhere, we probably won't see any increasing in the numbers. > Vhost-net is an example, and lots of optimizations have proved that virtio > ring is not the main bottleneck for the current codes. I suspect it also the > case of virtio driver. Did perf tell us any interesting things in virtio > driver? > > Thanks > > > > > > > > > > > On Wed, Jul 11, 2018 at 10:27:06AM +0800, Tiwei Bie wrote: > > > > > > Hello everyone, > > > > > > > > > > > > This patch set implements packed ring support in virtio driver. > > > > > > > > > > > > Some functional tests have been done with Jason's > > > > > > packed ring implementation in vhost: > > > > > > > > > > > > https://lkml.org/lkml/2018/7/3/33 > > > > > > > > > > > > Both of ping and netperf worked as expected. > > > > > > > > > > > > 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; > > > > > > > > > > > > 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/s390/virtio/virtio_ccw.c | 14 + > > > > > > drivers/virtio/virtio_ring.c | 1365 ++++++++++++++++++++++------ > > > > > > include/linux/virtio_ring.h | 8 +- > > > > > > include/uapi/linux/virtio_config.h | 3 + > > > > > > include/uapi/linux/virtio_ring.h | 43 + > > > > > > 5 files changed, 1157 insertions(+), 276 deletions(-) > > > > > > > > > > > > -- > > > > > > 2.18.0 > > > > > --------------------------------------------------------------------- > > > > > To unsubscribe, e-mail: virtio-dev-unsubscribe@xxxxxxxxxxxxxxxxxxxx > > > > > For additional commands, e-mail: virtio-dev-help@xxxxxxxxxxxxxxxxxxxx > > > > > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
