Enabling Virtual Machine support

Michael ODonnell michael.odonnell at comcast.net
Mon Sep 28 14:47:19 EDT 2009



> There was a study published a couple years back that showed
> enabling the VT instructions can result in lower performance

Heh.  The x86 instruction set offers some fancy instructions that are
supposed to help you implement an OS by doing (in one swell foop) some
fairly involved stuff like dumping all the CPU registers into memory as is
common during task switches.  I don't know if it's still true but early
on some of them were remarkably slower - IIRC sometimes something like
an order of magnitude slower - than an equivalent series of well chosen
"normal" instructions.
 


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