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Multi-process QEMU
==================
This document describes how to configure and use multi-process qemu.
For the design document refer to docs/devel/qemu-multiprocess.
1) Configuration
----------------
multi-process is enabled by default for targets that enable KVM
2) Usage
--------
Multi-process QEMU requires an orchestrator to launch.
Following is a description of command-line used to launch mpqemu.
* Orchestrator:
- 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
* Remote Process:
- 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,
* QEMU:
- Since parts of the RAM are shared between QEMU & remote process, a
memory-backend-memfd is required to facilitate this, as follows:
-object memory-backend-memfd,id=mem,size=2G
- 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:
-device x-pci-proxy-dev,id=lsi0,socket=3
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