fb929f78fb
Reviewed by: bcr Approved by: bcr Differential Revision: https://reviews.freebsd.org/D24915
169 lines
5.1 KiB
Groff
169 lines
5.1 KiB
Groff
.\"
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.\" Copyright (c) 2020, Gordon Bergling
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
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.\" ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd September 24, 2020
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.Dt TCP_BBR 4
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.Os
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.Sh NAME
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.Nm tcp_bbr
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.Nd TCP Bottleneck Bandwidth and Round-Trip Time Algorithm
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.Sh SYNOPSIS
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To use this TCP stack you have to place the following line in your
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kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "options TCPHPTS"
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.Ed
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.Pp
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To load the driver as a module at boot time, place the following line in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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tcp_bbr_load="YES"
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.Ed
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.Pp
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To enable the TCP stack you must place the following line in the
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.Xr sysctl.conf 5 :
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.Bd -literal -offset indent
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net.inet.tcp.functions_default=bbr
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.Ed
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.Sh DESCRIPTION
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Bottleneck bandwidth and round-trip time (BBR) is a congestion control algorithm which
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seeks high throughput with a small queue by probing BW and RTT.
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It is a round-up redesign of congestion control, which is not loss-based, delay-based,
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ECN-based or AIMD-based.
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.Pp
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The core design of BBR is about creating a model graph of the network path by
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estimating the maximum BW and minimum RTT on each ACK.
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.Sh MIB Variables
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The algorithm exposes the following scopes in the
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.Va net.inet.tcp.bbr
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branch of the
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.Xr sysctl 3
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MIB:
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.Bl -tag -width ".Va exp_backoff_scale"
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.It Va cwnd
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Cwnd controls, for example "target cwnd rtt measurment" and "BBR initial window".
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.It Va measure
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Measurement controls.
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.It Va pacing
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Connection pacing controls.
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.It Va policer
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Policer controls, for example "false detection threshold" and "loss threshold".
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.It Va probertt
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Probe RTT controls.
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.It Va startup
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Startup controls.
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.It Va states
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State controls.
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.It Va timeout
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Time out controls.
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.El
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.Pp
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Besides the variables within the above scopes the following
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variables are also exposed in the
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.Va net.inet.tcp.bbr
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branch:
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.Bl -tag -width ".Va exp_backoff_scale"
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.It Va clrlost
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Clear lost counters.
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.It Va software_pacing
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Total number of software paced flows.
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.It Va hdwr_pacing
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Total number of hardware paced flows.
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.It Va enob_no_hdwr_pacing
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Total number of enobufs for non-hardware paced flows.
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.It Va enob_hdwr_pacing
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Total number of enobufs for hardware paced flows.
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.It Va rtt_tlp_thresh
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What divisor for TLP rtt/retran will be added (1=rtt, 2=1/2 rtt etc).
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.It Va reorder_fade
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Does reorder detection fade, if so how many ms (0 means never).
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.It Va reorder_thresh
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What factor for rack will be added when seeing reordering (shift right).
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.It Va bb_verbose
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Should BBR black box logging be verbose.
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.It Va sblklimit
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When do we start ignoring small sack blocks.
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.It Va resend_use_tso
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Can resends use TSO?
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.It Va data_after_close
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Do we hold off sending a RST until all pending data is ack'd.
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.It Va kill_paceout
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When we hit this many errors in a row, kill the session?
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.It Va error_paceout
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When we hit an error what is the min to pace out in usec's?
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.It Va cheat_rxt
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Do we burst 1ms between sends on retransmissions (like rack)?
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.It Va minrto
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Minimum RTO in ms.
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.El
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.Sh SEE ALSO
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.Xr cc_chd 4 ,
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.Xr cc_cubic 4 ,
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.Xr cc_hd 4 ,
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.Xr cc_htcp 4 ,
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.Xr cc_newreno 4 ,
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.Xr cc_vegas 4 ,
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.Xr h_ertt 4 ,
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.Xr mod_cc 4 ,
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.Xr tcp 4 ,
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.Xr mod_cc 9
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.Rs
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.%A "Neal Cardwell"
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.%A "Yuchung Cheng"
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.%A "Stephen Gunn"
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.%A "Soheil Hassas Yeganeh"
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.%A "Van Jacobson"
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.%T "BBR: Congestion-Based Congestion Control"
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.%J "ACM Queue, Vol. 14"
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.%D "September / October 2016"
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.Re
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.Rs
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.%A "Dominik Scholz"
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.%A "Benedikt Jaeger"
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.%A "Lukas Schwaighofer"
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.%A "Daniel Raumer"
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.%A "Fabien Geyer"
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.%A "Georg Carle"
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.%T "Towards a Deeper Understanding of TCP BBR Congestion Control"
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.%J "IFIP Networking 2018"
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.%D "May 2018"
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.%U "http://www.net.in.tum.de/fileadmin/bibtex/publications/papers/IFIP-Networking-2018-TCP-BBR.pdf"
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.Re
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.Sh HISTORY
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The
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.Nm
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congestion control module first appeared in
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.Fx 13.0 .
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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congestion control module was written by
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.An Randall Stewart Aq Mt rrs@FreeBSD.org
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and sponsored by Netflix, Inc.
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This manual page was written by
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.An Gordon Bergling Aq Mt gbe@FreeBSD.org .
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