Memory bandwidth degradation of Armv8 virtualization

[Chris Hofer]

Hi everyone,

I'm currently measuring the memory bandwidth of the Genode Armv8 Linux 
Virtualization by running tinymembench[1] and lmbench's memory 
bandwidth[2]. On the NXP I.mx8 the results of both benchmarks showed a 
degradation of roughly 25 to 35 percent (depending on the exact 
benchmark) compared to native Linux.

I tried to ensure comparability with the native setup by disabling in 
native Linux all but one core and fixing this core's frequency to 1 GHz 
(which should be the frequency Genode uses). Both setups use the same 
Kernel version.

To improve the performance I played with the register values controlling 
caching (clear HCR_EL2.CD - enable S2 Data cacheability; VTCR_EL2.Irgn0 
and VTCR_EL2.Orgn0 respectively set to b11 - set Normal memory, 
Inner/Outer Write-Back Read-allocate No Write-Allocate Cachable). 
However, this had no significant effect.

What's your opinion on that? Based on your experience with 
virtualization, do these values surprise you or is this an expected 
degradation?

All the best,
Chris

[1] https://github.com/ssvb/tinymembench
[2] http://lmbench.sourceforge.net/
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