On Tue, Apr 20, 2021 at 10:56:56PM +0200, Toke Høiland-Jørgensen wrote: > Martin KaFai Lau <kafai@xxxxxx> writes: > > > On Thu, Apr 15, 2021 at 09:53:17PM +0800, Hangbin Liu 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: > >> > >> 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. > > (side note, while we're modifying the commit message, this paragraph > should probably be moved to the end) > > >> Using 10Gb i40e NIC, 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 > > Based on the discussion in v7, a summary of what still needs to be > > addressed will be useful. > > That's fair. How about we add a paragraph like this (below the one I > just suggested above that we move to the end): > > 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. > Clearing this up will be done in a separate patch series. lgtm
