This document describes how to configure and use multi-process qemu. For the design document refer to docs/devel/qemu-multiprocess.
multi-process is enabled by default for targets that enable KVM
Multi-process QEMU requires an orchestrator to launch.
Following is a description of command-line used to launch mpqemu.
- The Orchestrator creates a unix socketpair
- It launches the remote process and passes one of the sockets to it via command-line.
- It then launches QEMU and specifies the other socket as an option to the Proxy device object
QEMU can enter remote process mode by using the “remote” machine option.
The orchestrator creates a “remote-object” with details about the device and the file descriptor for the device
The remaining options are no different from how one launches QEMU with devices.
Example command-line for the remote process is as follows:
/usr/bin/qemu-system-x86_64 -machine x-remote -device lsi53c895a,id=lsi0 -drive id=drive_image2,file=/build/ol7-nvme-test-1.qcow2 -device scsi-hd,id=drive2,drive=drive_image2,bus=lsi0.0,scsi-id=0 -object x-remote-object,id=robj1,devid=lsi0,fd=4,
Since parts of the RAM are shared between QEMU & remote process, a memory-backend-memfd is required to facilitate this, as follows:
A “x-pci-proxy-dev” device is created for each of the PCI devices emulated in the remote process. A “socket” sub-option specifies the other end of unix channel created by orchestrator. The “id” sub-option must be specified and should be the same as the “id” specified for the remote PCI device
Example commandline for QEMU is as follows: