On Thu, 13 May 2021 15:04:44 +0800 Hangbin Liu <liuhangbin@xxxxxxxxx> wrote: > From: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> > > This changes the devmap XDP program support to run the program when the > bulk queue is flushed instead of before the frame is enqueued. This has > a couple of benefits: > > - It "sorts" the packets by destination devmap entry, and then runs the > same BPF program on all the packets in sequence. This ensures that we > keep the XDP program and destination device properties hot in I-cache. > > - It makes the multicast implementation simpler because it can just > enqueue packets using bq_enqueue() without having to deal with the > devmap program at all. > > The drawback is that if the devmap program drops the packet, the enqueue > step is redundant. However, arguably this is mostly visible in a > micro-benchmark, and with more mixed traffic the I-cache benefit should > win out. The performance impact of just this patch is as follows: > > Using 2 10Gb i40e NIC, redirecting one to another, or into a veth interface, > which do XDP_DROP on veth peer. With xdp_redirect_map in sample/bpf, send > pkts via pktgen cmd: > ./pktgen_sample03_burst_single_flow.sh -i eno1 -d $dst_ip -m $dst_mac -t 10 -s 64 > > There are about +/- 0.1M deviation for native testing, the performance > improved for the base-case, but some drop back with xdp devmap prog attached. > > Version | Test | Generic | Native | Native + 2nd xdp_prog > 5.12 rc4 | xdp_redirect_map i40e->i40e | 1.9M | 9.6M | 8.4M > 5.12 rc4 | xdp_redirect_map i40e->veth | 1.7M | 11.7M | 9.8M > 5.12 rc4 + patch | xdp_redirect_map i40e->i40e | 1.9M | 9.8M | 8.0M > 5.12 rc4 + patch | xdp_redirect_map i40e->veth | 1.7M | 12.0M | 9.4M > > When bq_xmit_all() is called from bq_enqueue(), another packet will > always be enqueued immediately after, so clearing dev_rx, xdp_prog and > flush_node in bq_xmit_all() is redundant. Move the clear to __dev_flush(), > and only check them once in bq_enqueue() since they are all modified > together. > > This change also has the side effect of extending the lifetime of the > RCU-protected xdp_prog that lives inside the devmap entries: Instead of > just living for the duration of the XDP program invocation, the > reference now lives all the way until the bq is flushed. This is safe > because the bq flush happens at the end of the NAPI poll loop, so > everything happens between a local_bh_disable()/local_bh_enable() pair. > However, this is by no means obvious from looking at the call sites; in > particular, some drivers have an additional rcu_read_lock() around only > the XDP program invocation, which only confuses matters further. > Cleaning this up will be done in a separate patch series. > > Acked-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> > Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> > Signed-off-by: Hangbin Liu <liuhangbin@xxxxxxxxx> For the sake of good order Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
