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Re: Request for New PPC Machine Supporting Multiple SMP Cores


From: BALATON Zoltan
Subject: Re: Request for New PPC Machine Supporting Multiple SMP Cores
Date: Thu, 7 Dec 2023 20:10:21 +0100 (CET)

On Thu, 7 Dec 2023, Peter Maydell wrote:
On Thu, 7 Dec 2023 at 17:40, BALATON Zoltan <balaton@eik.bme.hu> wrote:

On Thu, 7 Dec 2023, aziz tlili wrote:
Dear QEMU Team,

I hope this message finds you well. I've been a user of QEMU for well over
a year.

I wanted to share an idea for a potential enhancement that I believe could
benefit many users, including myself. It would be fantastic to have a new
PPC machine model similar to the existing mac99, but with support for
multiple SMP cores for both qemu-system-ppc and qemu-system-ppc64.

There are several machines in qemu-system-ppc64 that support SMP such as
pseries and powernv I think. For qemu-system-ppc maybe only ppce500. The
mac99 may create multiple CPUs (G4 when ron with qemu-system-ppc or G5
with qemu-system-ppc64) but not sure if there's an OS that can actually
use that. Linux support for mac99 may not be the best.

I think our mac99 machine refuses to create more than one CPU, because
it sets mc->max_cpus to 1 in core99_machine_class_init(). This in

Right. I remembered there was some quirk about that but it still has a loop when creating CPUs that's then apparently disabled. I've tried to send patches before to detangle this machine a bit as it also behaves differently depending if it's called from qemu-system-ppc or qemu-system-ppc64 or if machine properties are set which can be confusing but we could not agree on some naming so those patches were dropped at the end.

turn is probably because nobody has ever implemented and tested
whatever the SMP support handling would need to be for this machine
type.

It's likely that chipset support needed for SMP is missing although not sure how much of that would Linux need. So for now better try the others I've mentioned which may work better than mac99.

Problem is not in understanding the potential advantages but the lack of
people interested in working on that so progress depends on somebody doing
it and sending patches.

Entirely agreed. This is a feature request from two years ago about
adding SMP support to the newworld machines:
https://gitlab.com/qemu-project/qemu/-/issues/672
Nobody has done that work in two years, but anybody who has the
interest and time to do so is welcome to.

One thing that makes it a bit difficult is that there aren't much documentation available so those interested may need to consult Linux and XNU sources to find out what would need to be emulated.

Regards,
BALATON Zoltan



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