Resurrecting an old forgotten series... It should fix PPC64 issues with my recent "qemu: Store default CPU in domain XML" patches. On Tue, May 22, 2018 at 16:51:44 +0200, Andrea Bolognani wrote:
On Tue, 2018-05-22 at 15:46 +0200, Jiri Denemark wrote:
On Tue, May 22, 2018 at 11:02:17 +0200, Andrea Bolognani wrote:
On Thu, 2018-05-17 at 17:33 +0200, Jiri Denemark wrote: [...]
--- a/tests/domaincapsschemadata/qemu_2.12.0.ppc64.xml +++ b/tests/domaincapsschemadata/qemu_2.12.0.ppc64.xml @@ -25,7 +25,11 @@ <mode name='host-model' supported='yes'> <model fallback='allow'>POWER8</model> </mode>
This is quite suspicious - it looks like a proper CPU model, but it's really a compatibility mode, so it should be lowercase rather than uppercase. You certainly won't be able to use
<cpu mode='host-model> <model>POWER8</model> </cpu>
so why are we advertising the uppercase variant here? Am I missing something?
Actually the current way of reporting host-model in domain capabilities for ppc64 is not incorrect given the way domain capabilities are documented. <mode name='host-model' supported='yes'> <model fallback='allow'>POWER8</model> </mode> means <cpu mode='host-model'> CPU definition can be used in domain XML and the CPU model corresponding to the host CPU is POWER8. This is not supposed to be translated to <cpu mode='host-model'> <model>POWER8</model> </cpu> The interpretation of the domain capabilities snippet is either <cpu mode='host-model'/> or <cpu mode='custom' match='exact'> <model>POWER8</model> </cpu> And both will work, although the first one will not do what a user would expect due to the way host-model is misused for ppc. There's just no way of reporting this misuse in domain capabilities now. Perhaps we will come up with a way to solve this in the future. But we can stick with the current state now. ...
You have a point. The current situation is a bit confusing, again because of the misuse of host-model, but it's probably better to stick with the confusing situation we've grown used to rather than change things around for cosmetic reasons.
Plus, it's already strongly recommended to use
<cpu mode='host-model'> <model>power8</model> </cpu>
rather than
<cpu mode='custom'> <model>POWER8</model> </cpu>
because the resulting QEMU command line is more idiomatic, so applications and users sticking with the best practices wouldn't benefit from the change either way.
I disagree on having a mixture of uppercase and lowercase model, though: that's just bad UI, and a clear violation of the principle of least surprise; if and when a 'power10' CPU model will be added to QEMU, we should introduce a suitable 'POWER10' alias along with the existing ones.
OK, we can revisit this discussion later when a new power CPU model is introduced. I'll rebase this series on current master and resend it. Jirka