[Qemu-devel] [Bug 1824768] Re: Qemu ARMv7 TCG MultiThreading for i386 guest doesn't work

[Richard Henderson]

When you say

> ./qemu-system-i386 -cdrom alpine.iso --accel tcg,thread=multi

you have not created multiple cpus for the guest, so thread=multi
should have no effect.

For what it's worth, a boot of debian-9.8.0-i386-netinst.iso
(which is what I happened to have handy) works fine with 

  ./qemu-system-i386 -cdrom ... -m 1G --accel tcg,thread=multi

on an x-gene system, compiled for aarch32.

You should note that the default memory allocation is only 128MB,
and I'd be surprised if you can boot the alpine installation in
that little memory.  Certainly it does not work with debian.
On the other hand, the failure is a simple guest kernel panic
and not any kind of Illegal Instruction.

I'll try again in a moment with a cortex-a15 system, but I'm
not expecting any different result.

Just so we're clear, which raspberry pi revision are you using?
Based on comments I'm assuming pi 2, with the 4 core cortex-a7.

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https://bugs.launchpad.net/bugs/1824768

Title:
  Qemu ARMv7 TCG MultiThreading for i386 guest doesn't work

Status in QEMU:
  New

Bug description:
  Using any Linux image (in this case Alpine Linux iso) I want to
  utilise all cores of my Raspberry with --accel,thread=multi. I know
  there is a probably still problem with memory ordering of the host,
  but I have also seen some very old commits which could potentially
  help with it.

  But anyway, with version qemu-i386 version 3.1.0 (Debian 1:3.1+dfsg-7)
  I can see OpenRC starting up services and then the kernel crash.

  With version QEMU emulator version 3.1.93 (v4.0.0-rc3-dirty)
  The whole machine crash with this error:
  Illegal instruction

  Using command:
  ./qemu-system-i386 -cdrom alpine.iso --accel tcg,thread=multi

  Full Console Output:
  qemu-system-i386: warning: Guest expects a stronger memory ordering than the 
host provides
  This may cause strange/hard to debug errors
  Illegal instruction

  Kernel:
  Linux raspberrypi 4.14.98-v7+ #1200 SMP Tue Feb 12 20:27:48 GMT 2019 armv7l 
GNU/Linux

  CPU:
  ARMv7 Processor rev 5 (v7l)
  Features: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt 
vfpd32 lpae evtstrm
  4 cores

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