From: Jonathan Rajotte Date: Mon, 24 Jul 2017 20:07:00 +0000 (-0400) Subject: Fix live-comm: merge TCP socket write-write sequence in a single write X-Git-Tag: v2.11.0-rc1~506 X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=commitdiff_plain;h=b6025e9476332b75eb8184345c3eb3e924780088;hp=b6025e9476332b75eb8184345c3eb3e924780088 Fix live-comm: merge TCP socket write-write sequence in a single write The live protocol implementation is often sending content on TCP sockets in two separate writes. One to send a command header, and the second one sending the command's payload. This was presumably done under the assumption that it would not result in two separate TCP packets being sent on the network (or that it would not matter). Delayed ACK-induced delays were observed [1] on the second write of the "write header, write payload" sequence and result in problematic latency build-ups for live clients connected to moderately/highly active sessions. Fundamentaly, this problem arises due to the combination of Nagle's algorithm and the delayed ACK mechanism which make write-write-read sequences on TCP sockets problematic as near-constant latency is expected when clients can keep-up with the event production rate. In such a write-write-read sequence, the second write is held up until the first write is acknowledged (TCP ACK). The solution implemented by this patch bundles the writes into a single one [2]. [1] https://github.com/tbricks/wireshark-lttng-plugin Basic Wireshark dissector for lttng-live by Anto Smyk from Itiviti [2] https://lists.freebsd.org/pipermail/freebsd-net/2006-January/009527.html Reported-by: Anton Smyk Signed-off-by: Jonathan Rajotte Signed-off-by: Jérémie Galarneau ---