Discussion:
TCP RTT estimate for connections not using timestamps
(too old to reply)
Jacques Fourie
2018-10-31 14:04:44 UTC
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Hi,


While testing with traffic generators that don’t enable the TCP timestamp
option I noticed a couple of cases where tcp_xmit_timer() was called with a
0 value for rtt with the current smoothed rtt (t_srtt) non zero. This leads
to a left shift of -1 which is undefined. Looking at the code for the case
where timestamps are enabled I see that tcp_xmit_timer() is always called
with TCP_TS_TO_TICKS(t) + 1 for the rtt. Do we need a +1 in the non
timestamp case as well?


Thanks,

Jacques
Bjoern A. Zeeb
2018-10-31 14:11:58 UTC
Permalink
Post by Jacques Fourie
Hi,
While testing with traffic generators that don’t enable the TCP timestamp
option I noticed a couple of cases where tcp_xmit_timer() was called with a
0 value for rtt with the current smoothed rtt (t_srtt) non zero. This leads
to a left shift of -1 which is undefined. Looking at the code for the case
where timestamps are enabled I see that tcp_xmit_timer() is always called
with TCP_TS_TO_TICKS(t) + 1 for the rtt. Do we need a +1 in the non
timestamp case as well?
Thanks,
Jacques
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