(we were stuck on 3.18) ◦ fusion-io, sfc / ixgbe, netmap, glb-redirect ◦ custom patches (EPOLL_RR, SO_BINDTOPREFIX, XDP features) • hardware issues ◦ microcode bugs ◦ driver regressions • regressions ◦ SO_FILTER https://www.spinics.net/lists/netdev/msg555565.html ◦ nf_conncount https://www.spinics.net/lists/netfilter-devel/msg57316.html ◦ nf_nat_cleanup_conntrack https://bugzilla.kernel.org/show_bug.cgi?id=196821 ◦ systemd disabling TSO https://blog.cloudflare.com/tracing-system-cpu-on-debian-stretch/