| 1 | <?xml version='1.0' encoding='UTF-8'?>
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| 2 | <!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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| 3 | <topic xml:lang="en-us" id="changetscmode">
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| 4 | <title>Configuring the Guest Time Stamp Counter (TSC) to Reflect Guest
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| 5 | Execution</title>
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| 6 |
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| 7 | <body>
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| 8 | <p>
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| 9 | By default, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> keeps all sources of time visible to
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| 10 | the guest synchronized to a single time source, the monotonic
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| 11 | host time. This reflects the assumptions of many guest operating
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| 12 | systems, which expect all time sources to reflect "wall clock"
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| 13 | time. In special circumstances it may be useful however to make
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| 14 | the time stamp counter (TSC) in the guest reflect the time
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| 15 | actually spent executing the guest.
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| 16 | </p>
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| 17 | <p>
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| 18 | This special TSC handling mode can be enabled on a per-VM basis,
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| 19 | and for best results must be used only in combination with
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| 20 | hardware virtualization. To enable this mode use the following
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| 21 | command:
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| 22 | </p>
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| 23 | <pre xml:space="preserve">$ VBoxManage setextradata <varname>VM-name</varname> "VBoxInternal/TM/TSCTiedToExecution" 1</pre>
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| 24 | <p>
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| 25 | To revert to the default TSC handling mode use:
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| 26 | </p>
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| 27 | <pre xml:space="preserve">$ VBoxManage setextradata <varname>VM-name</varname> "VBoxInternal/TM/TSCTiedToExecution"</pre>
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| 28 | <p>
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| 29 | Note that if you use the special TSC handling mode with a guest
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| 30 | operating system which is very strict about the consistency of
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| 31 | time sources you may get a warning or error message about the
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| 32 | timing inconsistency. It may also cause clocks to become
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| 33 | unreliable with some guest operating systems depending on how
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| 34 | they use the TSC.
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| 35 | </p>
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| 36 | </body>
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| 37 |
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| 38 | </topic>
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