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authorNandita Dukkipati <nanditad@google.com>2011-08-21 20:21:57 +0000
committerDavid S. Miller <davem@davemloft.net>2011-08-24 19:40:40 -0700
commita262f0cdf1f2916ea918dc329492abb5323d9a6c (patch)
tree976cd31c3ea365f5810a154a1c77c75fb299c5fe /include/linux/tcp.h
parentf6fb8f100b807378fda19e83e5ac6828b638603a (diff)
Proportional Rate Reduction for TCP.
This patch implements Proportional Rate Reduction (PRR) for TCP. PRR is an algorithm that determines TCP's sending rate in fast recovery. PRR avoids excessive window reductions and aims for the actual congestion window size at the end of recovery to be as close as possible to the window determined by the congestion control algorithm. PRR also improves accuracy of the amount of data sent during loss recovery. The patch implements the recommended flavor of PRR called PRR-SSRB (Proportional rate reduction with slow start reduction bound) and replaces the existing rate halving algorithm. PRR improves upon the existing Linux fast recovery under a number of conditions including: 1) burst losses where the losses implicitly reduce the amount of outstanding data (pipe) below the ssthresh value selected by the congestion control algorithm and, 2) losses near the end of short flows where application runs out of data to send. As an example, with the existing rate halving implementation a single loss event can cause a connection carrying short Web transactions to go into the slow start mode after the recovery. This is because during recovery Linux pulls the congestion window down to packets_in_flight+1 on every ACK. A short Web response often runs out of new data to send and its pipe reduces to zero by the end of recovery when all its packets are drained from the network. Subsequent HTTP responses using the same connection will have to slow start to raise cwnd to ssthresh. PRR on the other hand aims for the cwnd to be as close as possible to ssthresh by the end of recovery. A description of PRR and a discussion of its performance can be found at the following links: - IETF Draft: http://tools.ietf.org/html/draft-mathis-tcpm-proportional-rate-reduction-01 - IETF Slides: http://www.ietf.org/proceedings/80/slides/tcpm-6.pdf http://tools.ietf.org/agenda/81/slides/tcpm-2.pdf - Paper to appear in Internet Measurements Conference (IMC) 2011: Improving TCP Loss Recovery Nandita Dukkipati, Matt Mathis, Yuchung Cheng Signed-off-by: Nandita Dukkipati <nanditad@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/tcp.h')
-rw-r--r--include/linux/tcp.h4
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 531ede8006d9..6b63b310af36 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -379,6 +379,10 @@ struct tcp_sock {
u32 snd_cwnd_clamp; /* Do not allow snd_cwnd to grow above this */
u32 snd_cwnd_used;
u32 snd_cwnd_stamp;
+ u32 prior_cwnd; /* Congestion window at start of Recovery. */
+ u32 prr_delivered; /* Number of newly delivered packets to
+ * receiver in Recovery. */
+ u32 prr_out; /* Total number of pkts sent during Recovery. */
u32 rcv_wnd; /* Current receiver window */
u32 write_seq; /* Tail(+1) of data held in tcp send buffer */