Digital Garden

Lima

Lima or Linux on Mac

Can be used to run a linux virtual machine on mac.
Colima actually uses lima to first start a linux virtual machine, and then run docker inside it.

This article is a summary of my observations from various experiments I conducted with lima. It might be a little unstructured, so bare with me.

VMTypes and their performance

Main article: https://lima-vm.io/docs/config/vmtype
Lima supports 2 VMTypes: QEMU and VZ

QEMU

Repo: https://gitlab.com/qemu-project/qemu

The OG emulator, open source, cross platform.

Although QEMU can do a lot of emulations, in lima, its used mainly for 2 purposes:

  1. qemu-x86_64: To emulate an x86_64 linux
  2. qemu-arch64: To emulate an arch64 linux

If you run htop on host (mac), you will see the qemu-system process corresponding to the VM that you are running.

QEMU supports both userspace emulation and entire machine (hardware) level emulation. But I guess Lima defaults to the machine level emulation.

Refer to the diagram in the this article for summary of what to use when

From my experiments, running an x86_64 Ubuntu VM on on M1 Mac using QEMU was very slow, which is also expected since this is cross-architecture run.
Although I need to look for benchmarks comparing same-architecture performance of QEMU on Mac (intel vs M1).

VZ

Repo: https://github.com/Code-Hex/vz

VZ is a new and faster emulator specifically for Mac because VZ uses Apple’s native virtualization API .

If you run htop on host (mac), you will see the AppleVirtualizationFramework process running corresponding to the VM.

VZ is still experimental. Lima falls back to QEMU if VZ requirements are not met.

VZ will become the default VMType once lima reaches v1.0

But I guess based on this diagram, VZ only does userspace emulation. The way it works is VZ requires a VM which is of same architecture as the host mac ( todo need to verify this ). So we can’t specify a different architecture using --arch when --vmtype vz is passed. Then it translates the system calls on the VM to MacOS kernel calls.

On M1 macs, although the VM OS will always be aarch64 linux, one can enable Rosetta 2 to run x86_64 containers inside aarch64 linux. In lima this is done by passing --vz-rosetta option. The containers can run in a different architecture using docker’s --platform option.

Can intel mac run aarch64 containers using VZ? todo

Benchmarks

Here is a benchmark on 2020 M1 Macbook Air, ran by Josh Byranes
https://github.com/ctrlok/macdockergeek/issues/3

Graph View