Date: Fri, 13 Jul 2012 10:54:35 -0700 From: Reese Faucette <reese@myri.com> To: freebsd-net@freebsd.org Subject: question in tcp_do_segment() Message-ID: <500060DB.3090407@myri.com> In-Reply-To: <4FFF9E48.6000403@myri.com> References: <4FFF9E48.6000403@myri.com>
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Hi, freebsd-net- I don't have a testcase for this at the moment, but there's a test in tcp_do_segment that looks backwards to me... http://svnweb.freebsd.org/base/release/9.0.0/sys/netinet/tcp_input.c?view=markup line 2398 - if (!tcp_timer_active(tp, TT_REXMT) || th->th_ack != tp->snd_una) tp->t_dupacks = 0; says "If we get a DUP ack and the retransmit timer is NOT fired, then ignore it and reset DUP ACK count." Isn't that exactly backwards? I could see ignoring the DUP ACK if we know the retransmit timer HAS fired, and we don't want to interfere with its retransmission efforts. The way the code is written now, as far as I can see, completely defeats retransmission based on DUP acks. I accidentally ran across this by breaking the timer, so that the retransmit timer never fires, and my streams get stuck, even with plenty of DUP ACKs. Am I missing something, or should that "!" go ? Thanks, Reese Faucette Myricom, Inc.
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