From: David Miller <davem@davemloft.net>
To: yinglinsun@cs.pitt.edu
Cc: netdev@vger.kernel.org
Subject: Re: [TCP_CA_CWR] Causes for entering TCP_CA_CWR state with 0 retransmissions
Date: Tue, 14 Jul 2009 12:15:28 -0700 (PDT) [thread overview]
Message-ID: <20090714.121528.15246520.davem@davemloft.net> (raw)
In-Reply-To: <46bf9ede0907141212x7a7a84f8l1882ffefbaf21e14@mail.gmail.com>
From: Yinglin Sun <yinglinsun@cs.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.
next prev parent reply other threads:[~2009-07-14 19:15 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-14 18:38 [TCP_CA_CWR] Causes for entering TCP_CA_CWR state with 0 retransmissions Yinglin Sun
2009-07-14 18:42 ` David Miller
2009-07-14 19:12 ` Yinglin Sun
2009-07-14 19:15 ` David Miller [this message]
2009-07-14 19:49 ` Yinglin Sun
2009-07-14 19:53 ` David Miller
2009-07-14 19:58 ` Yinglin Sun
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