[Discuss] virtualization overhead

[Rich Pieri]

On Sun, 5 Aug 2012 07:47:49 -0700
Rich Braun <richb at pioneer.ci.net> wrote:
> As for how it could be possible: CPU performance far exceeds that of
> any current I/O. So emulation overhead drops way below the roughly 3%
> CPU overhead that I recall measuring. Throw a big RAM cache
> underneath your VM, and you can get blazing fast numbers.

Ah-hah!  Yes.  If you cache I/O then you bypass the trap and emulate
latency.  You will see similar performance on bare metal.  But you did
stipulate not caching I/O so as to avoid data loss in case of a power
failure.  If you take the cache away then performance drops to the
disk and controller at which point you should see a small but
measurable performance hit on the emulated controller.  If you don't
then there's probably still some caching going on somewhere.

-- 
Rich P.