mirror of https://github.com/schoebel/mars
doc: lowlevel TCP tuning
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Thomas Schoebel-Theuer
Thomas Schoebel-Theuer
parent
d5dc1ea8af
commit
5111c76103
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@ -34598,6 +34598,217 @@ demand
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running.
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\end_layout
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\begin_layout Subsection
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Lowlevel TCP Tuning (Networking Experts Only)
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\begin_inset CommandInset label
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LatexCommand label
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name "subsec:TCP-Tuning"
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\end_inset
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\end_layout
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\begin_layout Standard
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MARS uses the following types of traffic:
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\end_layout
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\begin_layout Description
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\family typewriter
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MARS_TRAFFIC_META
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\family default
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(by default on port 7777 with
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\family typewriter
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IPTOS_LOWDELAY
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\family default
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) This can be tuned in directory
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\family typewriter
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/proc/sys/mars/tcp_tuning_0_meta_traffic/
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\family default
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.
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\end_layout
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\begin_layout Description
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\family typewriter
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MARS_TRAFFIC_REPLICATION
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\family default
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(by default on port 7778 with
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\family typewriter
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IPTOS_RELIABILITY
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\family default
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) This can be tuned in directory
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\family typewriter
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/proc/sys/mars/tcp_tuning_1_replication_traffic/
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\family default
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.
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\end_layout
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\begin_layout Description
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\family typewriter
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MARS_TRAFFIC_SYNC
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\family default
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(by default on port 7779 with
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\family typewriter
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IPTOS_MINCOST
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\family default
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) This can be tuned in directory
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\family typewriter
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/proc/sys/mars/tcp_tuning_2_sync_traffic/
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\family default
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.
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Attention: since the advent of
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\family typewriter
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DSCP
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\family default
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, this bit (hex
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\family typewriter
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0x2
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\family default
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in host byte order) is suppressed by the kernel, and yields
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\family typewriter
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DS0
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\family default
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.
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\end_layout
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\begin_layout Standard
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In each of these directories, the following tunables are available (only
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for networking experts who know what they are doing):
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\end_layout
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\begin_layout Description
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\family typewriter
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ip_tos
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\family default
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As explained above.
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Notice: hex constants from
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\family typewriter
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/usr/include/linux/ip.h
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\family default
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must be converted to decimal before forwarding to the
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\family typewriter
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/proc
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\family default
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interface.
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\end_layout
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\begin_layout Description
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\family typewriter
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tcp_window_size
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\family default
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Current default is 8 * 1024 * 1024.
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\end_layout
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\begin_layout Description
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\family typewriter
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tcp_nodelay
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\family default
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Current default is 0.
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\end_layout
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\begin_layout Description
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\family typewriter
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tcp_timeout
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\family default
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Current default is 2.
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\end_layout
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\begin_layout Description
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\family typewriter
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tcp_keepcnt
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\family default
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Current default is 3.
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\end_layout
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\begin_layout Description
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\family typewriter
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tcp_keepintvl
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\family default
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Current default is 3.
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\end_layout
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\begin_layout Description
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\family typewriter
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tcp_keepidle
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\family default
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Current default is 4.
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\end_layout
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\begin_layout Standard
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\noindent
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\begin_inset Graphics
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filename images/lightbulb_brightlit_benj_.png
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lyxscale 12
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scale 7
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\end_inset
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Further tuning parameters are in the standard Linux kernel.
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Notice that
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\family typewriter
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IP_TOS
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\family default
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is internally converted to
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\family typewriter
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DSCP
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\family default
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, which in turn can be further manipulated by
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\family typewriter
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netfilter
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\family default
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/
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\family typewriter
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iptables
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\family default
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and/or by
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\family typewriter
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qdisc
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\family default
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(
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\family typewriter
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tc
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\family default
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) and/or by further (external) networking components.
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The ancient TOS settings are meant as a default
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\emph on
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starting point
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\emph default
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for further customization to your needs.
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\end_layout
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\begin_layout Standard
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\noindent
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\begin_inset Graphics
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filename images/MatieresCorrosives.png
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lyxscale 50
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scale 17
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\end_inset
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Playing with these settings can easily tear down your whole (replication)
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network if you don't know exactly what you are doing.
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Please test any changes in the lab first.
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Mass rollout should be done in incremental phases, each in power of 10
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units.
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There might be unexpected effects like packet storms, or packet loss, etc.
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Some of these effects may only show up when a certain number of hosts is
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exceeded, or when certain load conditions are hammering the overall Distributed
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System.
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Some very old routers / switches are known to break down unexpectedly when
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overloaded in certain ways.
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Be careful in a production environment!
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\end_layout
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\begin_layout Chapter
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Tips and Tricks
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\end_layout
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