Re: debian bootup hangs on qemu-system-mips64el

[Paul Burton <paulburton@kernel.org>]

Hi Jun Sun,

On Sun, Jan 12, 2020 at 06:14:12PM -0800, Jun Sun wrote:
> On Sun, Jan 12, 2020 at 11:58 AM Aurelien Jarno <aurelien@aurel32.net> wrote:
> > On 2020-01-12 11:34, Jun Sun wrote:
> > > Are you sure QEMU/MIPS does not support SMP?  Below link written in
> > > 2016 clearly shows something was working then.
> > >
> > > https://www.mips.com/blog/how-to-run-smp-linux-in-qemu-on-a-mips64-release-6-cpu/
> >
> > It's not supported for the malta/mips64r2 combination you are trying to
> > use. It's clearly possible that it is supported for mips64r6, but it's a
> > different instruction set, so you can't run a standard Debian
> > distribution on it.
> 
> How do I specify mips64r6 cpu to start qemu?  A simple cpu listing
> below shows no such CPU.  If mips64r6 is indeed supported with SMP, I
> would think mips64r2 userland should run fine.

I know that using QEMU's I6400 or I6500 CPU emulation works fine with
SMP as far as -smp 8. It emulates a single core system with up to 8 VPs
(hardware threads), and Linux works fine with it. I most often use the
Boston board emulation with a 64r6el_defconfig kernel for this, but it
ought to work for Malta too.

Both I6400 & I6500 are MIPS64r6 CPUs, so as Aurelien said you'd need to
ensure you're using a suitable MIPSr6 root filesystem.

If you wanted to run as I do it'd go something like this:

$ qemu-system-mips64el \
    -M boston \
    -cpu I6500 \
    -smp 8 \
    -kernel arch/mips/boot/vmlinux.gz.itb

Where that's run from the root of a kernel source tree within which
you've built a 64r6el_defconfig kernel.

Not sure what the behavior is with older CPUs; QEMU's CM & CPC emulation
is somewhat incomplete, and whilst I6400 & I6500 have a relatively
straightforward VP model older CPUs have the more complex MT ASE with
VPEs & TCs to worry about.

Thanks,
    Paul