This patch set aims to improve how TCP handle local qdisc congestion by simplifying the previous implementation. Previously when an skb fails to (re)transmit due to local qdisc congestion or other resource issue, TCP refrains from setting the skb timestamp or the recovery starting time.
This design makes determining when to abort a stalling socket more complicated, as the timestamps of these tranmission attempts were missing. The stack needs to sort of infer when the original attempt happens. A by-product is a socket may disregard the system timeout limit (i.e. sysctl net.ipv4.tcp_retries2 or USER_TIMEOUT option), and continue to retry until the transmission is successful. In data-center environment when TCP RTO is small, this could cause the socket to retry frequently for long during qdisc congestion. The solution is to first unconditionally timestamp skb and recovery attempt. Then retry more conservatively (twice a second) on local qdisc congestion but abort the sockets according to the system limit. Yuchung Cheng (8): tcp: exit if nothing to retransmit on RTO timeout tcp: always timestamp on every skb transmission tcp: always set retrans_stamp on recovery tcp: properly track retry time on passive Fast Open tcp: create a helper to model exponential backoff tcp: simplify window probe aborting on USER_TIMEOUT tcp: retry more conservatively on local congestion tcp: less aggressive window probing on local congestion net/ipv4/tcp_output.c | 47 ++++++++++-------------- net/ipv4/tcp_timer.c | 83 ++++++++++++++++++------------------------- 2 files changed, 54 insertions(+), 76 deletions(-) -- 2.20.1.97.g81188d93c3-goog
