Interesting running it in QEMU. If possible, it might be better to use a container if the host kernel supports this because performance and resource consumption should both be significantly improved.
However, an emulator provides great flexibility I’ll give you that.
It is pretty cool! QEMU can do all kinds of interesting things, although I do wish it had better performance. High performance doesn’t appear to be a primary goal for QEMU outside of using KVM.
You need hardware acceleration for any ki.d of performance. Without it you are just emulating which means you needs lots of hardware instructions for a few emulator instructions
Yes indeed. I develop QEMU at work mainly implementation of new hardware as needed for my employer. It has a software emulator, but it’s not very good. It’s acceptable.
The instruction generation backend does not seem to prioritize performance. Instead, it prioritizes accuracy and ease of maintenance. There is low-hanging fruit for making it faster but there isn’t much interest in doing so for the TCG backend. The attitude seems to be that it’s good enough.
For a small example, you may find it interesting that QEMU does not implement floating point acceleration. It’s done in software even though the host has floating point instructions. It usually doesn’t attempt to use those floating point hardware facilities on the host and instead execute many hundreds of instructions to do floating point using the Berkeley software implementation. Almost never does this matter but it costs a lot of performance. Compare this to the translation performed by projects like FEX and Box64 which do and blow QEMU out of the water for specific use cases.
Another place in the emulator that could be improved is handling of executable pages or cached output of the backend code generator. The executable code caching mechanism is very simple and could probably be much more aggressive on today’s systems.
If you examine change logs, TCG really doesn’t get much TLC last time I checked. It could be a better emulator but performance outside of KVM use case is not as important to the project.
QEMU absolutely will use hardware floating point where it can but only when it will give the correct results. FEX and Box64 are user mode emulators which achieve their speed by avoiding emulation where they can buy thunking at API boundaries.
It’s worth noting if you are using this on an arm device, this isn’t a “virtualization VM” any more, as you are using the emulator backend, so this is far closer to a traditional emulator then anything else.
While the term virtual machine is extremely poorly defined, it could still apply.
also TCG is as slow as molasses, it’s a good demo, not actually usable for much, at least unless it’s a super beefy phone.
Looks like it’s an x86_64 kernel though? So this is a VM - it’s not running as a paravirtualised system, it’s having to emulate everything from the CPU up?