On Mon, Sep 27, 2021 at 1:30 PM Johannes Lundberg <jlundberg@xxxxxxxx> wrote:
The EPOLLEMPTY event will trigger when the TCP write buffer becomes
empty, i.e., when all outgoing data have been ACKed.
The need for this functionality comes from a business requirement
of measuring with higher precision how much time is spent
transmitting data to a client. For reference, similar functionality
was previously added to FreeBSD as the kqueue event EVFILT_EMPTY.
Adding yet another indirect call  in TCP fast path, for something
(measuring with higher precision..)
which is already implemented differently in TCP stack  is not desirable.
Our timestamping infrastructure should be ported to FreeBSD instead :)
 Refs :
net-timestamp: ACK timestamp for bytestreams