| Message ID | 20210218204908.5455-1-alobakin@pm.me |
|---|---|
| Headers | show |
| Series | xsk: build skb by page (aka generic zerocopy xmit) | expand |
On 2/18/21 9:49 PM, Alexander Lobakin wrote: > This series introduces XSK generic zerocopy xmit by adding XSK umem > pages as skb frags instead of copying data to linear space. > The only requirement for this for drivers is to be able to xmit skbs > with skb_headlen(skb) == 0, i.e. all data including hard headers > starts from frag 0. > To indicate whether a particular driver supports this, a new netdev > priv flag, IFF_TX_SKB_NO_LINEAR, is added (and declared in virtio_net > as it's already capable of doing it). So consider implementing this > in your drivers to greatly speed-up generic XSK xmit. [...] Applied, thanks!
This series introduces XSK generic zerocopy xmit by adding XSK umem pages as skb frags instead of copying data to linear space. The only requirement for this for drivers is to be able to xmit skbs with skb_headlen(skb) == 0, i.e. all data including hard headers starts from frag 0. To indicate whether a particular driver supports this, a new netdev priv flag, IFF_TX_SKB_NO_LINEAR, is added (and declared in virtio_net as it's already capable of doing it). So consider implementing this in your drivers to greatly speed-up generic XSK xmit. The first bit adds missing IFF self-definition. It's a bit out, but "while we are here". The fourth patch adds headroom and tailroom reservations for the allocated skbs on XSK generic xmit path. This ensures there won't be any unwanted skb reallocations on fast-path due to headroom and/or tailroom driver/device requirements (own headers/descriptors etc.). The other three add a new private flag, declare it in virtio_net driver and introduce generic XSK zerocopy xmit itself. The main body of work is created and done by Xuan Zhuo. His original cover letter: v3: Optimized code v2: 1. add priv_flags IFF_TX_SKB_NO_LINEAR instead of netdev_feature 2. split the patch to three: a. add priv_flags IFF_TX_SKB_NO_LINEAR b. virtio net add priv_flags IFF_TX_SKB_NO_LINEAR c. When there is support this flag, construct skb without linear space 3. use ERR_PTR() and PTR_ERR() to handle the err v1 message log: --------------- This patch is used to construct skb based on page to save memory copy overhead. This has one problem: We construct the skb by fill the data page as a frag into the skb. In this way, the linear space is empty, and the header information is also in the frag, not in the linear space, which is not allowed for some network cards. For example, Mellanox Technologies MT27710 Family [ConnectX-4 Lx] will get the following error message: mlx5_core 0000:3b:00.1 eth1: Error cqe on cqn 0x817, ci 0x8, qn 0x1dbb, opcode 0xd, syndrome 0x1, vendor syndrome 0x68 00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00000030: 00 00 00 00 60 10 68 01 0a 00 1d bb 00 0f 9f d2 WQE DUMP: WQ size 1024 WQ cur size 0, WQE index 0xf, len: 64 00000000: 00 00 0f 0a 00 1d bb 03 00 00 00 08 00 00 00 00 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00000020: 00 00 00 2b 00 08 00 00 00 00 00 05 9e e3 08 00 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 mlx5_core 0000:3b:00.1 eth1: ERR CQE on SQ: 0x1dbb I also tried to use build_skb to construct skb, but because of the existence of skb_shinfo, it must be behind the linear space, so this method is not working. We can't put skb_shinfo on desc->addr, it will be exposed to users, this is not safe. Finally, I added a feature NETIF_F_SKB_NO_LINEAR to identify whether the network card supports the header information of the packet in the frag and not in the linear space. ---------------- Performance Testing ------------ The test environment is Aliyun ECS server. Test cmd: ``` xdpsock -i eth0 -t -S -s <msg size> ``` Test result data: size 64 512 1024 1500 copy 1916747 1775988 1600203 1440054 page 1974058 1953655 1945463 1904478 percent 3.0% 10.0% 21.58% 32.3%