Eyes Above The Waves

Thursday 5 November 2015

rr In VMWare: Solved!

Well, sort of.

I previously explained how rr running in a VMWare guest encounters a VMWare bug where performance counters measuring conditional branches executed fail to count a conditional branch executed between a pair of CPUID instructions. Today a helpful VWMare developer confirmed that this is an issue caused by clever optimizations in the virtual machine monitor. Better still, he provided an easy way to work around it! Just add

monitor_control.disable_hvsim_clusters = true

to your .vmx file. This may impact guest performance a little bit, but it will make rr work reliably in a VMWare guest, which should be useful to a lot of people. Excellent!