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authorlstewart <lstewart@FreeBSD.org>2011-02-21 11:56:11 +0000
committerlstewart <lstewart@FreeBSD.org>2011-02-21 11:56:11 +0000
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Final commit to round out the "Five New TCP Congestion Control Algorithms for
FreeBSD" FreeBSD Foundation funded project. - Add new man pages for the modular congestion control, Khelp and Hhook frameworks (cc.4, cc.9, khelp.9 and hhook.9). - Add new man pages for each available congestion control algorithm (cc_chd.4, cc_cubic.4, cc_hd.4, cc_htcp.4, cc_newreno.4 and cc_vegas.4). - Add a new man page for the Enhanced Round Trip Time (ERTT) Khelp module (h_ertt.4). - Update the TCP (tcp.4) man page to mention the TCP_CONGESTION socket option, cross reference to cc.4 and remove references to the retired "net.inet.tcp.newreno" sysctl MIB variable. In collaboration with: David Hayes <dahayes at swin edu au> and Grenville Armitage <garmitage at swin edu au> Sponsored by: FreeBSD Foundation MFC after: 3 months
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+.\"
+.\" Copyright (c) 2010-2011 The FreeBSD Foundation
+.\" All rights reserved.
+.\"
+.\" This documentation was written at the Centre for Advanced Internet
+.\" Architectures, Swinburne University, Melbourne, Australia by David Hayes
+.\" under sponsorship from the FreeBSD Foundation.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\" notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\" notice, this list of conditions and the following disclaimer in the
+.\" documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
+.\" ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd February 15, 2011
+.Dt h_ertt 9
+.Os
+.Sh NAME
+.Nm h_ertt
+.Nd Enhanced Round Trip Time Khelp module
+.Sh SYNOPSIS
+.In netinet/khelp/h_ertt.h
+.Sh DESCRIPTION
+The
+.Nm
+Khelp module works within the
+.Xr khelp 9
+framework to provide TCP with a per-connection, low noise estimate of the
+instantaneous RTT.
+The implementation attempts to be robust in the face of delayed
+acknowledgements, TCP Segmentation Offload (TSO), receivers who manipulate TCP
+timestamps and lack of the TCP timestamp option altogether.
+.Pp
+TCP receivers using delayed acknowledgements either acknowledge every second packet
+(reflecting the time stamp of the first) or use a timeout to trigger the
+acknowledgement if no second packet arrives.
+If the heuristic used by
+.Nm
+determines that the receiver is using delayed acknowledgements, it measures the
+RTT using the second packet (the one that triggers the acknowledgement).
+It does not measure the RTT if the acknowledgement is for the
+first packet, since it cannot be accurately determined.
+.Pp
+When TSO is in use,
+.Nm
+will momentarily disable TSO whilst marking a packet to use for a new
+measurement.
+The process has negligible impact on the connection.
+.Pp
+.Nm
+associates the following struct with each connection's TCP control block:
+.Bd -literal
+struct ertt {
+ TAILQ_HEAD(txseginfo_head, txseginfo) txsegi_q; /* Private. */
+ long bytes_tx_in_rtt; /* Private. */
+ long bytes_tx_in_marked_rtt;
+ unsigned long marked_snd_cwnd;
+ int rtt;
+ int maxrtt;
+ int minrtt;
+ int dlyack_rx; /* Private. */
+ int timestamp_errors; /* Private. */
+ int markedpkt_rtt; /* Private. */
+ uint32_t flags;
+};
+.Ed
+.Pp
+The fields marked as private should not be manipulated by any code outside of
+the
+.Nm
+implementation.
+The non-private fields provide the following data:
+.Bl -tag -width ".Va bytes_tx_in_marked_rtt" -offset indent
+.It Va bytes_tx_in_marked_rtt
+The number of bytes transmitted in the
+.Va markedpkt_rtt .
+.It Va marked_snd_cwnd
+The value of cwnd for the marked rtt measurement.
+.It Va rtt
+The most recent RTT measurement.
+.It Va maxrtt
+The longest RTT measurement that has been taken.
+.It Va minrtt
+The shortest RTT measurement that has been taken.
+.It Va flags
+The ERTT_NEW_MEASUREMENT flag will be set by the implementation when a new
+measurement is available.
+It is the responsibility of
+.Nm
+consumers to unset the flag if they wish to use it as a notification method for
+new measurements.
+.El
+.Sh SEE ALSO
+.Xr cc 4 ,
+.Xr cc_chd 4 ,
+.Xr cc_hd 4 ,
+.Xr cc_vegas 4 ,
+.Xr hhook 9 ,
+.Xr khelp 9
+.Sh ACKNOWLEDGEMENTS
+Development and testing of this software were made possible in part by grants
+from the FreeBSD Foundation and Cisco University Research Program Fund at
+Community Foundation Silicon Valley.
+.Sh HISTORY
+The
+.Nm
+module first appeared in
+.Fx 9.0 .
+.Pp
+The module was first released in 2010 by David Hayes whilst working on the
+NewTCP research project at Swinburne University's Centre for Advanced Internet
+Architectures, Melbourne, Australia.
+More details are available at:
+.Pp
+http://caia.swin.edu.au/urp/newtcp/
+.Sh AUTHORS
+.An -nosplit
+The
+.Nm
+Khelp module and this manual page were written by
+.An David Hayes Aq david.hayes@ieee.org .
+.Sh BUGS
+The module maintains enhanced RTT estimates for all new TCP connections created
+after the time at which the module was loaded.
+It might be beneficial to see if it is possible to have the module only affect
+connections which actually care about ERTT estimates.
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