netdev - Re: [TCP_CA_CWR] Causes for entering TCP_CA

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Message-Id: <20090714.121528.15246520.davem@davemloft.net>
Date:	Tue, 14 Jul 2009 12:15:28 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	yinglinsun@...pitt.edu
Cc:	netdev@...r.kernel.org
Subject: Re: [TCP_CA_CWR] Causes for entering TCP_CA_CWR state with 0
 retransmissions

From: Yinglin Sun <yinglinsun@...pitt.edu>
Date: Tue, 14 Jul 2009 15:12:16 -0400

> I use the total number of retransmissions reported by tcp_info. The
> field name is tcpi_total_retrans. From the kernel source code, I found
> that this number is for both fast retransmit and timeout
> retransmissions. On the other hand, if fast retransmission happened,
> ca_state should be TCP_CA_Recovery or TCP_CA_Disorder, but it's
> TCP_CA_CWR.

Great, that if you're reading the code you also see that there
are many code paths that invoke tcp_enter_cwr() that can occur
without any retransmissions. :-)

One such case is when ECN congestion notification bits are
seen in an ACK packet.
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