Fast UNIX Servers
Everyone ought start with Dan Kegel's classic site, "The C10K Problem" (still updated from time to time). Everything here is advanced followup material to Dan's excellent work.
- http://lkml.indiana.edu/hypermail/linux/kernel/0101.3/0674.html "sendfile(): fairly sexy (nothing to do with ECN)" on lkml
- http://unix.derkeiler.com/Mailing-Lists/FreeBSD/hackers/2005-12/msg00105.html "mmap() sendfile()" on freebsd-hackers