Long ago, the storage representations of srtt and rttvar were changed
from the 4.4BSD scheme, and the comments are out of sync with the
code. This commit rewrites most of the comments that explain the RTO
calculations, and points out some issues in the code.
Joint work with Bev Schwartz of BBN (original analysis and comments),
but I have rewritten and extended them, so errors are mine.
This material is based upon work supported by the Defense Advanced
Research Projects Agency and Space and Naval Warfare Systems Center,
Pacific, under Contract No. N66001-09-C-2073. Approved for Public
Release, Distribution Unlimited
to break free of the constraint if the range minimum boundary is larger than
the maximum boundary.
Discovered by jmg@FreeBSD.org. (See FreeBSD's tcp_timer.h rev 1.31).
it in the TCP stack to test which of the REXMT or PERSIST timer is in use.
This fixes a race condition that could cause "panic: tcp_output REXMT". See
tech-net for details.
all open TCP connections in tcp_slowtimo() (which is called 2x
per second). It's fairly rare for TCP timers to actually fire,
so saving this list traversal is good, especially if you want
to scale to thousands of open connections.
and call it directly from tcp_slowtimo() (via a table) rather
than going through tcp_userreq().
This will allow us to call TCP timers directly from callouts,
in a future revision.
the protocol dispatch layer for TCP timers. This saves having to
modify a potentially large number of timer values (which were shorts,
and expanded to ... a lot of code on the Alpha).
gdt