cvs commit: src/sys/netinet tcp_subr.c tcp_timer.h

Peter Jeremy peterjeremy at
Wed Aug 1 08:38:03 UTC 2007

On 2007-Jul-31 22:11:56 +0000, Peter Wemm <peter at> wrote:
>  To demonstrate, boot with kern.hz=100.  ssh to a box on local ethernet
>  and establish a reliable round-trip-time (ie: type a few commands).
>  Then unplug the ethernet and press a key.  Time how long it takes to
>  drop the connection.

I've bumped into this problem as well but chose a slightly different
solution.  I've left the TCPTV_MIN/tcp_rexmit_min code alone (because
I believed the bit about it being scaled to hz).  Instead I added a
new sysctl "Minimum Retransmission Period before Dropping Connection"
and require that a connection's t_rxtshift remain at TCP_MAXRXTSHIFT
until that time has expired.

My gut feeling is that putting an artifical lower bound on the RTT is
a hackish way to control the retransmit timeout - I thought the TCP
algorithms relied on knowing the real RTT to correctly handle
retransmissions.  A variable that explicitly controls the retransmit
timeout would seem easier to understand.

I thought I'd PR'd the patch but it looks like I haven't.  If anyone
is interested, I'll submit it.

Peter Jeremy
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