diff options
author | 2011-07-03 09:55:03 -0600 | |
---|---|---|
committer | 2011-07-04 12:37:49 -0600 | |
commit | 113ced1f52e5ed2dfedc0771a1b11b536cde8168 (patch) | |
tree | 513df4ef1ad8b8530e12329f8f02c89140860b36 /net/dccp/ccids/ccid2.h | |
parent | dccp ccid-2: Use existing function to test for data packets (diff) | |
download | linux-113ced1f52e5ed2dfedc0771a1b11b536cde8168.tar.gz linux-113ced1f52e5ed2dfedc0771a1b11b536cde8168.tar.bz2 linux-113ced1f52e5ed2dfedc0771a1b11b536cde8168.zip |
dccp ccid-2: Perform congestion-window validation
CCID-2's cwnd increases like TCP during slow-start, which has implications for
* the local Sequence Window value (should be > cwnd),
* the Ack Ratio value.
Hence an exponential growth, if it does not reflect the actual network
conditions, can quickly lead to instability.
This patch adds congestion-window validation (RFC2861) to CCID-2:
* cwnd is constrained if the sender is application limited;
* cwnd is reduced after a long idle period, as suggested in the '90 paper
by Van Jacobson, in RFC 2581 (sec. 4.1);
* cwnd is never reduced below the RFC 3390 initial window.
As marked in the comments, the code is actually almost a direct copy of the
TCP congestion-window-validation algorithms. By continuing this work, it may
in future be possible to use the TCP code (not possible at the moment).
The mechanism can be turned off using a module parameter. Sampling of the
currently-used window (moving-maximum) is however done constantly; this is
used to determine the expected window, which can be exploited to regulate
DCCP's Sequence Window value.
This patch also sets slow-start-after-idle (RFC 4341, 5.1), i.e. it behaves like
TCP when net.ipv4.tcp_slow_start_after_idle = 1.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Diffstat (limited to 'net/dccp/ccids/ccid2.h')
-rw-r--r-- | net/dccp/ccids/ccid2.h | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/net/dccp/ccids/ccid2.h b/net/dccp/ccids/ccid2.h index da021ebce9af..f585d330e1e5 100644 --- a/net/dccp/ccids/ccid2.h +++ b/net/dccp/ccids/ccid2.h @@ -53,6 +53,10 @@ struct ccid2_seq { * @tx_rttvar: moving average/maximum of @mdev_max * @tx_rto: RTO value deriving from SRTT and RTTVAR (RFC 2988) * @tx_rtt_seq: to decay RTTVAR at most once per flight + * @tx_cwnd_used: actually used cwnd, W_used of RFC 2861 + * @tx_expected_wnd: moving average of @tx_cwnd_used + * @tx_cwnd_stamp: to track idle periods in CWV + * @tx_lsndtime: last time (in jiffies) a data packet was sent * @tx_rpseq: last consecutive seqno * @tx_rpdupack: dupacks since rpseq * @tx_av_chunks: list of Ack Vectors received on current skb @@ -76,6 +80,12 @@ struct ccid2_hc_tx_sock { u64 tx_rtt_seq:48; struct timer_list tx_rtotimer; + /* Congestion Window validation (optional, RFC 2861) */ + u32 tx_cwnd_used, + tx_expected_wnd, + tx_cwnd_stamp, + tx_lsndtime; + u64 tx_rpseq; int tx_rpdupack; u32 tx_last_cong; |