On Fri, Oct 13, 2017 at 1:03 PM, Cong Wang <xiyou.wangc...@gmail.com> wrote: > We need a real-time notification for tcp retransmission > for monitoring. > > Of course we could use ftrace to dynamically instrument this > kernel function too, however we can't retrieve the connection > information at the same time, for example perf-tools [1] reads > /proc/net/tcp for socket details, which is slow when we have > a lots of connections. > > Therefore, this patch adds a tracepoint for __tcp_retransmit_skb() > and exposes src/dst IP addresses and ports of the connection. > This also makes it easier to integrate into perf. > > Note, I expose both IPv4 and IPv6 addresses at the same time: > for a IPv4 socket, v4 mapped address is used as IPv6 addresses, > for a IPv6 socket, LOOPBACK4_IPV6 is already filled by kernel. > Also, add sk and skb pointers as they are useful for BPF.
Thanks, a TCP retransmit tracepoint would be great. (tcp_set_state would be highly useful too, which Alexei already has in his list). Should skp->__sk_common.skc_state be included in the format string, so we don't have to always dig it out of the skaddr? For retransmits I always want to know the TCP state, to determine if it is ESTABLISHED (packet drop) or SYN_SENT (backlog full) or something else. We probably need a tracepoint for tcp_send_loss_probe() (TLP) as well, for tracing at the same time as retransmits (like my tools do), but that can be added later. Brendan
