From: Alexei Starovoitov Date: Fri, 31 May 2019 23:41:30 +0000 (-0700) Subject: Merge branch 'propagate-cn-to-tcp' X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=576240cfaf206ea7d08ae7421088a788d861212d;p=openwrt%2Fstaging%2Fblogic.git Merge branch 'propagate-cn-to-tcp' Lawrence Brakmo says: ==================== This patchset adds support for propagating congestion notifications (cn) to TCP from cgroup inet skb egress BPF programs. Current cgroup skb BPF programs cannot trigger TCP congestion window reductions, even when they drop a packet. This patch-set adds support for cgroup skb BPF programs to send congestion notifications in the return value when the packets are TCP packets. Rather than the current 1 for keeping the packet and 0 for dropping it, they can now return: NET_XMIT_SUCCESS (0) - continue with packet output NET_XMIT_DROP (1) - drop packet and do cn NET_XMIT_CN (2) - continue with packet output and do cn -EPERM - drop packet Finally, HBM programs are modified to collect and return more statistics. There has been some discussion regarding the best place to manage bandwidths. Some believe this should be done in the qdisc where it can also be managed with a BPF program. We believe there are advantages for doing it with a BPF program in the cgroup/skb callback. For example, it reduces overheads in the cases where there is on primary workload and one or more secondary workloads, where each workload is running on its own cgroupv2. In this scenario, we only need to throttle the secondary workloads and there is no overhead for the primary workload since there will be no BPF program attached to its cgroup. Regardless, we agree that this mechanism should not penalize those that are not using it. We tested this by doing 1 byte req/reply RPCs over loopback. Each test consists of 30 sec of back-to-back 1 byte RPCs. Each test was repeated 50 times with a 1 minute delay between each set of 10. We then calculated the average RPCs/sec over the 50 tests. We compare upstream with upstream + patchset and no BPF program as well as upstream + patchset and a BPF program that just returns ALLOW_PKT. Here are the results: upstream 80937 RPCs/sec upstream + patches, no BPF program 80894 RPCs/sec upstream + patches, BPF program 80634 RPCs/sec These numbers indicate that there is no penalty for these patches The use of congestion notifications improves the performance of HBM when using Cubic. Without congestion notifications, Cubic will not decrease its cwnd and HBM will need to drop a large percentage of the packets. The following results are obtained for rate limits of 1Gbps, between two servers using netperf, and only one flow. We also show how reducing the max delayed ACK timer can improve the performance when using Cubic. Command used was: ./do_hbm_test.sh -l -D --stats -N -r= [--no_cn] [dctcp] \ -s= where: is 1000 --no_cn specifies no cwr notifications dctcp uses dctcp Cubic DCTCP Lim, DA Mbps cwnd cred drops Mbps cwnd cred drops -------- ---- ---- ---- ----- ---- ---- ---- ----- 1G, 40 35 462 -320 67% 995 1 -212 0.05% 1G, 40,cn 736 9 -78 0.07 995 1 -212 0.05 1G, 5,cn 941 2 -189 0.13 995 1 -212 0.05 Notes: --no_cn has no effect with DCTCP Lim = rate limit DA = maximum delay ack timer cred = credit in packets drops = % packets dropped v1->v2: Insures that only BPF_CGROUP_INET_EGRESS can return values 2 and 3 New egress values apply to all protocols, not just TCP Cleaned up patch 4, Update BPF_CGROUP_RUN_PROG_INET_EGRESS callers Removed changes to __tcp_transmit_skb (patch 5), no longer needed Removed sample use of EDT v2->v3: Removed the probe timer related changes v3->v4: Replaced preempt_enable_no_resched() by preempt_enable() in BPF_PROG_CGROUP_INET_EGRESS_RUN_ARRAY() macro ==================== Acked-by: Martin KaFai Lau Signed-off-by: Alexei Starovoitov --- 576240cfaf206ea7d08ae7421088a788d861212d