Re: about the current status of Multi-process QEMU / out-of-process emulation

[Jag Raman]

On Jun 3, 2022, at 11:34 AM, Yu Zhang <yu.zhang@ionos.com> wrote:

Hello Dongli, Elena, John, and Jagannathan,

I'm interested in the "multi-process QEMU" feature and got the kind reply by Mr. Vivier that I may contact you for this.
On one of the QEMU docs [1] I saw the command line:

+      /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=lsi1,fd=4,

It seems that the man page of qemu contains no parameter and option yet for this feature. The qemu docs, such as [2][3][4] are either not up-to-date or "doesn't reflect the current status of the implementation". 

So may I know whether is it still in experimental stage or mature enough for use? And even a few further questions:

Hello Yu,

We are working on vfio-user for QEMU which would supersede multi-process QEMU.

The vfio-user feature is currently under review for merging with QEMU. We would drop

multi-process QEMU support after the vfio-user changes are merged.

We use the following repo for testing vfio-user before sending the patches for

review. You may be interested in checking it out:

https://github.com/oracle/qemu/tree/master

- When creating the orchestrator, can we specify a machine type such as pc-i440fx-7.0 for -machine?

For vfio-user, the machine type on the remote QEMU process (server) is

always “x-remote”. The client QEMU could be of any machine type.

- Can each device has a dedicated emulation process or shares one process for emulating multiple devices?

Each device could be running in a dedicated process, or multiple

devices could share one process.

- Can we find more command line examples showing the combination of orchestrator, remote emulation process, memory-backend-memfd and x-pci-proxy-dev?

For vfio-user, we could give you a heads up once they are merged into QEMU. We

are using the following for testing our changes, which you could checkout

in the meanwhile:

scripts/vfiouser-launcher.py 

Could you please give us more details about what you’re trying to do? Which

devices are you trying to emulate in the remote process?

Thank you!

--

Jag

Thank you very much and all the best

Yu Zhang
03.06.2022

[1] https://www.qemu.org/docs/master/system/multi-process.html

[2] https://wiki.qemu.org/Features/MultiProcessQEMU

[3] https://lxr.missinglinkelectronics.com/qemu+v7.0.0/docs/devel/multi-process.rst

[4] https://qemu.readthedocs.io/en/latest/devel/multi-process.html 

---------- Forwarded message ---------
From: Laurent Vivier <laurent@vivier.eu>
Date: Fri, Jun 3, 2022 at 4:14 PM
Subject: Re: about the current status of Multi-process QEMU / out-of-process emulation
To: Yu Zhang <yu.zhang@ionos.com>

Hi Yu,

I'm not the author of this documentation, only the person that has merged the last change in the repo.

According to the logs you should contact Dongli Zhang <dongli.zhang@oracle.com>, Elena Ufimtseva
<elena.ufimtseva@oracle.com>, John G Johnson <john.g.johnson@oracle.com> or Jagannathan Raman
<jag.raman@oracle.com> .

Thanks,
Laurent

Le 03/06/2022 à 12:17, Yu Zhang a écrit :
> Dear Mr. Vivier,
>
> I saw that you authored the QEMU page for "Multi-process QEMU".
> (https://www.qemu.org/docs/master/system/multi-process.html
> <https://www.qemu.org/docs/master/system/multi-process.html>)
>
> I'm interested in this feature, but feel a little confused with the command line:
>
> +      /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=lsi1,fd=4,
>
> It seems that the man page of qemu command contains no parameter and option yet for this feature.
> May I know whether is it still in experimental stage? And even a few more questions:
>
> - Is "x-remote" a standalone machine type for creating the orchestrator?
> - Can each device has a dedicated emulation process or shares one process for emulating multiple
> devices?
> - Can I find more command line examples illustrating the combination of orchestrator, remote
> emulation process, memory-backend-memfd and x-pci-proxy-dev?
>
> Thank you very much
> Kind regard
>
> Yu Zhang
> 03.06.2022