v3: ~ Separate EOR marking from the SKBTX_ANY_TSTAMP logic. ~ Move the eor bit test back to the loop in tcp_sendmsg and tcp_sendpage because there could be >1 threads doing sendmsg. ~ Thanks to Eric Dumazet's suggestions on v2. ~ The TCP timestamp bug fixes are separated into other threads.
v2: ~ Rework based on the recent work "add TX timestamping via cmsg" by Soheil Hassas Yeganeh <soheil.k...@gmail.com> ~ This version takes the MSG_EOR bit as a signal of end-of-response-message and leave the selective timestamping job to the cmsg ~ Changes based on the v1 feedback (like avoid unlikely check in a loop and adding tcp_sendpage support) ~ The first 3 patches are bug fixes. The fixes in this series depend on the newly introduced txstamp_ack in net-next. I will make relevant patches against net after getting some feedback. ~ The test results are based on the recently posted net fix: "tcp: Fix SOF_TIMESTAMPING_TX_ACK when handling dup acks" ~ Due to the lacking cmsg support in packetdrill (or may be I just could not find it), a BPF prog is used to kprobe to sock_queue_err_skb() and print out the value of serr->ee.ee_data. The BPF prog (run-able from bcc) is attached at the end. One potential use case is to use MSG_EOR with SOF_TIMESTAMPING_TX_ACK to get a more accurate TCP ack timestamping on application protocol with multiple outgoing response messages (e.g. HTTP2). One of our use case is at the webserver. The webserver tracks the HTTP2 response latency by measuring when the webserver sends the first byte to the socket till the TCP ACK of the last byte is received. In the cases where we don't have client side measurement, measuring from the server side is the only option. In the cases we have the client side measurement, the server side data can also be used to justify/cross-check-with the client side data.
