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160 lines
4.9 KiB
Groff
160 lines
4.9 KiB
Groff
.\" SPDX-License-Identifier: BSD-2-Clause
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.\"
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.\" Copyright (c) 2022, Gordon Bergling <gbe@FreeBSD.org>
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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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.Dd March 19, 2023
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.Dt TCP_RACK 4
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.Os
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.Sh NAME
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.Nm tcp_rack
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.Nd TCP RACK-TLP Loss Detection Algorithm for TCP
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.Sh SYNOPSIS
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To use this TCP stack, place the following line in the
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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 TCP stack 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_rack_load="YES"
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.Ed
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.Pp
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To enable the TCP stack, 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=rack
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.Ed
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.Sh DESCRIPTION
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RACK-TLP uses per-segment transmit timestamps and selective
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acknowledgments (SACKs) and has two parts.
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Recent Acknowledgment (RACK) starts fast recovery quickly
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using time-based inferences derived from acknowledgment (ACK)
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feedback, and Tail Loss Probe (TLP) leverages RACK
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and sends a probe packet to trigger ACK feedback to avoid
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retransmission timeout (RTO) events.
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.Pp
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Compared to the widely used duplicate acknowledgment (DupAck)
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threshold approach, RACK-TLP detects losses more efficiently
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when there are application-limited flights of data, lost
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retransmissions, or data packet reordering events.
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.Pp
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It is intended to be an alternative to the
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DupAck threshold approach.
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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.rack
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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 indent
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.It Va net.inet.tcp.rack.misc
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Misc related controls
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.It Va net.inet.tcp.rack.features
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Feature controls
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.It Va net.inet.tcp.rack.measure
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Measure related controls
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.It Va net.inet.tcp.rack.timers
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Timer related controls
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.It Va net.inet.tcp.rack.tlp
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TLP and Rack related Controls
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.It Va net.inet.tcp.rack.timely
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Rack Timely RTT Controls
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.It Va net.inet.tcp.rack.hdwr_pacing
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Pacing related Controls
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.It Va net.inet.tcp.rack.pacing
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Pacing related Controls
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.It Va net.inet.tcp.rack.tp
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Rack tracepoint facility
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.It Va net.inet.tcp.rack.probertt
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ProbeRTT related Controls
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.It Va net.inet.tcp.rack.stats
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Rack Counters
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.It Va net.inet.tcp.rack.sack_attack
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Rack Sack Attack Counters and 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.rack
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branch:
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.Bl -tag -width indent
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.It Va net.inet.tcp.rack.clear
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Clear counters
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.It Va net.inet.tcp.rack.opts
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RACK Option Stats
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.It Va net.inet.tcp.rack.outsize
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MSS send sizes
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.It Va net.inet.tcp.rack.req_measure_cnt
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If doing dynamic pacing, how many measurements
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must be in before we start pacing?
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.It Va net.inet.tcp.rack.use_pacing
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If set we use pacing, if clear we use only the original burst mitigation
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.It Va net.inet.tcp.rack.rate_sample_method
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What method should we use for rate sampling 0=high, 1=low
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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 tcp_bbr 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 "Nandita Dukkipat"
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.%A "Priyaranjan Jha"
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.%T "The RACK-TLP Loss Detection Algorithm for TCP"
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.%O "RFC 8985"
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.%D "February 2021"
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.Re
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.Rs
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.%A "Ahmed M. Abdelmoniem"
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.%A "Brahim Bensaou"
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.%T "T-RACKs: A Faster Recovery Mechanism for TCP in Data Center Networks"
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.%O "https://arxiv.org/abs/2102.07477"
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.%D "February 2021"
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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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