mirror of https://github.com/schoebel/mars
doc: move control model
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Thomas Schoebel-Theuer
Thomas Schoebel-Theuer
parent
47544459f0
commit
6d5f412728
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@ -141,6 +141,163 @@ LatexCommand tableofcontents
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Basic Working Principle
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\end_layout
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\begin_layout Section
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Control Model
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\begin_inset CommandInset label
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LatexCommand label
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name "sec:Control-Model"
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\end_inset
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\end_layout
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\begin_layout Standard
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Although MARS tries to
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\emph on
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approximate
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\emph default
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/
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\emph on
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emulate
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\emph default
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the synchronous control behaviour of DRBD at the interface level (
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\family typewriter
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marsadm
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\family default
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) in many situations as best as it can, the
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\emph on
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internal
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\emph default
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control model is necessarily asynchronous.
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As an experiencend sysadmin, you will be curious how it works in principle.
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When you know something about it, you will no longer be surprised when
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some (detail) behaviour is different from DRBD.
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\end_layout
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\begin_layout Standard
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The general principle is an asynchronous 2-edge handshake protocol, which
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is used almost everywhere in MARS:
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\begin_inset Separator latexpar
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\end_inset
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\end_layout
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\begin_layout Standard
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\noindent
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\align center
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\begin_inset Graphics
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filename images/handshake.fig
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width 80col%
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\end_inset
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\end_layout
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\begin_layout Standard
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We have a binary todo switch, which can be either in state
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\begin_inset Quotes eld
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\end_inset
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on
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\begin_inset Quotes erd
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\end_inset
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or
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\begin_inset Quotes eld
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\end_inset
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off
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\begin_inset Quotes erd
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\end_inset
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.
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In addition, we have an actual response indicator, which is similar to
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an LED indicating the actual status.
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In our example, we imagine that both are used for controlling a big ventilator,
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having a huge inert mass.
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Imagine a big machine from a power plant, which is as tall as a human.
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\end_layout
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\begin_layout Standard
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We start in a situation where the binary switch is off, and the ventilator
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is stopped.
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At point 1, we turn on the switch.
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At that moment, a big contactor will sound like
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\begin_inset Quotes eld
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\end_inset
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zonggg
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\begin_inset Quotes erd
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\end_inset
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, and a big motor will start to hum.
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At first you won't hear anything else.
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It will take a while, say 1 minute, until the big wheel will have reached
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its final operating RPM, due to the huge inert mass.
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During that spin-up, the lights in your room will become slightly darker.
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When having reached the full RPM at point 2, your workplace will then be
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noisier, but in exchange your room lights will be back at ordinary strength,
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and the actual response LED will start to lit in order to indicate that
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the big fan is now operational.
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\end_layout
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\begin_layout Standard
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Assume we want to turn the system off.
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When turning the todo switch to
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\begin_inset Quotes eld
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\end_inset
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off
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\begin_inset Quotes erd
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\end_inset
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at point 3, first nothing will seem to happen at all.
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The big wheel will keep spinning due to its heavy inert mass, and the RPM
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as well as the sound will go down only slowly.
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During spin-down, the actual response LED will stay illuminated, in order
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to warn you that you should not touch the wheel, otherwise you may get
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injuried
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\begin_inset Foot
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status open
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\begin_layout Plain Layout
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Notice that it is only safe to access the wheel when
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\emph on
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both
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\emph default
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the switch and the LED are off.
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Conversely, if at least one of them is on, something is going on inside
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the machine.
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Transferred to MARS: always look at
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\emph on
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both
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\emph default
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the todo switch and the correponding actual indicator in order to not miss
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something.
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\end_layout
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\end_inset
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.
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The LED will only go off after, say, 2 minutes, when the wheel has actually
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stopped at point 4.
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After that, the cycle may potentially start over again.
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\end_layout
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\begin_layout Standard
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As you can see, all four possible cartesian product combinations between
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two boolean values are occurring in the diagram.
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\end_layout
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\begin_layout Standard
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The same handshake protocol is used in MARS for communication between userspace
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and kernelspace, as well as for communication in the widely distributed
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system.
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\end_layout
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\begin_layout Section
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The Lamport Clock
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\begin_inset CommandInset label
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@ -32021,152 +32021,6 @@ Old Structure (TO DISAPPEAR)
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Quick Start Guide
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\end_layout
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\begin_layout Standard
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Although MARS tries to
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\emph on
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approximate
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\emph default
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/
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\emph on
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emulate
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\emph default
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the synchronous control behaviour of DRBD at the interface level (
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\family typewriter
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marsadm
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\family default
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) in many situations as best as it can, the
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\emph on
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internal
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\emph default
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control model is necessarily asynchronous.
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As an experiencend sysadmin, you will be curious how it works in principle.
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When you know something about it, you will no longer be surprised when
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some (detail) behaviour is different from DRBD.
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\end_layout
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\begin_layout Standard
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The general principle is an asynchronous 2-edge handshake protocol, which
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is used almost everywhere in MARS:
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\begin_inset Separator latexpar
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\end_inset
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\end_layout
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\begin_layout Standard
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\noindent
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\align center
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\begin_inset Graphics
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filename images/handshake.fig
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width 80col%
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\end_inset
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\end_layout
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\begin_layout Standard
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We have a binary todo switch, which can be either in state
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\begin_inset Quotes eld
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\end_inset
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on
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\begin_inset Quotes erd
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\end_inset
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or
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\begin_inset Quotes eld
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\end_inset
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off
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\begin_inset Quotes erd
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\end_inset
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.
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In addition, we have an actual response indicator, which is similar to
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an LED indicating the actual status.
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In our example, we imagine that both are used for controlling a big ventilator,
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having a huge inert mass.
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Imagine a big machine from a power plant, which is as tall as a human.
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\end_layout
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\begin_layout Standard
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We start in a situation where the binary switch is off, and the ventilator
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is stopped.
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At point 1, we turn on the switch.
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At that moment, a big contactor will sound like
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\begin_inset Quotes eld
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\end_inset
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zonggg
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\begin_inset Quotes erd
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\end_inset
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, and a big motor will start to hum.
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At first you won't hear anything else.
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It will take a while, say 1 minute, until the big wheel will have reached
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its final operating RPM, due to the huge inert mass.
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During that spin-up, the lights in your room will become slightly darker.
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When having reached the full RPM at point 2, your workplace will then be
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noisier, but in exchange your room lights will be back at ordinary strength,
|
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and the actual response LED will start to lit in order to indicate that
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the big fan is now operational.
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\end_layout
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\begin_layout Standard
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Assume we want to turn the system off.
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When turning the todo switch to
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\begin_inset Quotes eld
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\end_inset
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off
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\begin_inset Quotes erd
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\end_inset
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at point 3, first nothing will seem to happen at all.
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The big wheel will keep spinning due to its heavy inert mass, and the RPM
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as well as the sound will go down only slowly.
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During spin-down, the actual response LED will stay illuminated, in order
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to warn you that you should not touch the wheel, otherwise you may get
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injuried
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\begin_inset Foot
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status open
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\begin_layout Plain Layout
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Notice that it is only safe to access the wheel when
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\emph on
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both
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\emph default
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the switch and the LED are off.
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Conversely, if at least one of them is on, something is going on inside
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the machine.
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Transferred to MARS: always look at
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\emph on
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both
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\emph default
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the todo switch and the correponding actual indicator in order to not miss
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something.
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\end_layout
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\end_inset
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.
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The LED will only go off after, say, 2 minutes, when the wheel has actually
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stopped at point 4.
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After that, the cycle may potentially start over again.
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\end_layout
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\begin_layout Standard
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As you can see, all four possible cartesian product combinations between
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two boolean values are occurring in the diagram.
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\end_layout
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\begin_layout Standard
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The same handshake protocol is used in MARS for communication between userspace
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and kernelspace, as well as for communication in the widely distributed
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system.
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\end_layout
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\begin_layout Chapter
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||||
Basic Working Principle
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\end_layout
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|
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