Re: [Qemu-devel] [Qemu-ppc] [PATCH] target-ppc: Change default machine for 64-bit

[Andreas Färber]

Am 13.06.2013 15:49, schrieb Alexander Graf:
> On 17.05.2013, at 09:42, Andreas Färber wrote:
>> Am 17.05.2013 06:25, schrieb David Gibson:
>>> Currently, for qemu-system-ppc64, the default machine type is 'mac99'.
>>> Since the mac99 machine is not being actively maintained, and shows quite
>>> a few signs of bitrot,
>>
>> Please be more specific than making such general claims in a commit
>> message! As the default machine it certainly compiles, so where are you
>> seeing bitrot? The DEC bridge cleanup that I once started kind of
>> depends on the PCI cleanup you recently looked into.
> 
> The mac99 machine for 64bit is actually worse than anything bitrot could give 
> you. It emulates a machine that in its form never possibly could have existed 
> in real hardware, which makes it very fragile and dependent on the guest's 
> mercy to handle this gracefully.

Still we should put that in the commit message and not "shows quite a
few signs of bitrot". Bitrot is what gus.c and cs4231a.c may have
endured while not being compiled in or those disabled DPRINTF()s
sprinkled all over the code base.

Further, David is looking at this from a biased perspective: -M pseries
is best maintained (apart from e500) ppc target, but it doesn't work
with PR KVM (not on my box anyway). But neither does mac99 on KVM due to
page sizes or something IIRC. However under TCG either is okay with the
guests I've seen so far and they all compile warning-free.

pseries used to hang, that is no longer the case, it just doesn't do
anything now - still need to debug how to improve that.

> Given the current state and amount of development on the pseries target, I 
> think it makes sense to declare that as the default for qemu-system-ppc64.

No disagreement there then.

Andreas

> I would still love to see -M mac99 emulate a proper U2 or U1 based system for 
> 32bit. And I would also love to see a real U4 based emulation model come up 
> for qemu-system-ppc64. But I doubt I'll have time to work on either :).
> 
> 
> Alex

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