| 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>By default, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> keeps all sources of time visible to the guest
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| 9 | synchronized to a single time source, the monotonic host time. This reflects the assumptions of many guest
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| 10 | operating systems, which expect all time sources to reflect "wall clock" time. In special circumstances it may be
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| 11 | useful however to make the time stamp counter (TSC) in the guest reflect the time actually spent executing the
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| 12 | guest. </p>
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| 13 | <p>This special TSC handling mode can be enabled on a per-VM basis, and for best results must be used only in
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| 14 | combination with hardware virtualization. To enable this mode use the following command: </p>
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| 15 | <pre xml:space="preserve">$ VBoxManage setextradata <varname>VM-name</varname> "VBoxInternal/TM/TSCTiedToExecution" 1</pre>
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| 16 | <p>To revert to the default TSC handling mode use: </p>
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| 17 | <pre xml:space="preserve">$ VBoxManage setextradata <varname>VM-name</varname> "VBoxInternal/TM/TSCTiedToExecution"</pre>
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| 18 | <p>Note that if you use the special TSC handling mode with a guest operating system which is very strict about the
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| 19 | consistency of time sources you may get a warning or error message about the timing inconsistency. It may also
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| 20 | cause clocks to become unreliable with some guest operating systems depending on how they use the TSC. </p>
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| 21 | </body>
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| 22 |
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| 23 | </topic>
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