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?
Hmm, you're right. In general, this is advertising the host CPU (ideally as seen by QEMU), which doesn't really work for ppc since host-model was misused for compatibility modes. I think we'll have to add a special hack to produce <mode name='host-model' supported='yes'/> without showing any CPU model. Ideally, we would somehow list all supported compatibility modes, but this can be left for the future.
Sounds good.
- <mode name='custom' supported='no'/> + <mode name='custom' supported='yes'> + <model usable='unknown'>POWER9</model> + <model usable='unknown'>POWER8</model> + <model usable='unknown'>POWER7</model> + </mode>
This is of course an improvement, but I'm not sure we want to keep exposing uppercase model names to users.
I understand we need to keep accepting them for compatibility reasons, but since QEMU has moved to lowercase CPU model names wouldn't it make sense for libvirt to follow suit?
I don't think so. Introducing new aliases (i.e., lower case variants) for the existing models would IMHO cause more troubles than having a mixture of upper case and lower case names (once something like power10 is introduced). Users or apps would have to use a crystal ball to check which CPU model name would be compatible with older libvirt.
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. -- Andrea Bolognani / Red Hat / Virtualization