L4Linux performance vs hardware virtualization

Hi Folks,

L4Linux.org mentioned:
 "Compared to monolithic Linux, there is a small performance tradeoff because of the µ-kernel architecture. However, the initial L4Linux has been somewhat optimized, and on L4/x86 it has a very acceptable slowdown of less than 4 % for any relevant load.
"
Any place can find more detail about the test?

And I'm very curious the L4Linux performance vs "using hardware virtualization on top of L4", have you made any comparison  before?

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Thank you!
Bob