On Mon, May 05, 2025 at 09:07:52AM -0300, Daniel Henrique Barboza wrote: > > > On 5/5/25 5:58 AM, Andrea Bolognani wrote: > > On Tue, Apr 29, 2025 at 05:41:43PM +0200, Jiří Denemark wrote: > > > On Tue, Apr 29, 2025 at 13:03:12 +0100, Daniel P. Berrangé wrote: > > > > On Tue, Apr 29, 2025 at 01:42:22PM +0200, Peter Krempa wrote: > > > > > On Tue, Apr 29, 2025 at 12:36:40 +0100, Daniel P. Berrangé wrote: > > > > > > On Tue, Apr 15, 2025 at 04:13:08AM -0400, Narayana Murty N wrote: > > > > > > > <model usable='unknown' vendor='IBM'>POWER7</model> > > > > > > > <model usable='unknown' vendor='IBM'>POWER8</model> > > > > > > > <model usable='unknown' vendor='IBM'>POWER9</model> > > > > > > > + <model usable='unknown' vendor='IBM'>power11</model> > > > > > > > > > > > > QEMU allows both upper & lowercase for CPU names, and libvirt > > > > > > has stuck with uppercase historically. > > > > > > > > > > > > What's the justification for changing this approach for > > > > > > power11 ? > > > > > > > > > > qemu itself reports the model lowercase now. In v2 of this series I've > > > > > pointed that out because defining this caused test data to change > > > > > which > > > > > was suspiciuous. > > > > > > > > By 'reports the model lowercase' i presume you're referring to '-cpu > > > > help' > > > > and/or 'query-cpu-definitions' ? That doesn't seem to be a new change > > > > either though. I've not gone far back, but qemu 8.2.0 seems to already > > > > be using lowercase. > > > > > > > > So I'm still wondering why we're changing our decision about CPU naming > > > > /now/ with power11 ? The commit message needs to explain and justify > > > > this change. > > > > > > Well, when I replied to the original patch, my memory was telling me > > > QEMU switched to lower case names and had to add compatibility code to > > > translate our existing upper case names. And adding a new CPU model > > > looked like a good excuse to stop doing that (for new models of course) > > > and just define the model in lower case. Now that you're questioning > > > this I tried to find evidence and I could not find it :-( So there are > > > two options... either I'm bad at searching or I my memory confused this > > > with dropping version suffixes (_vX.Y) in virCPUppc64ConvertLegacy. Or > > > both options are true at the same time :-) > > > > > > Maybe Andrea can remember more, I think he was involved in all this ages > > > ago. > > > > It seems that CPU models have been reported in lower case at least > > going all the way back to QEMU 3.0.0 from 2018: > > > > > > https://gitlab.com/libvirt/libvirt/-/blob/c7e09b7b5fe7f64f12318d150b281343c6d64fd5/tests/qemucapabilitiesdata/caps_3.0.0.ppc64.replies > > > > It would probably make sense for libvirt to align with this decision, > > and accept/generate lower case CPU model names. Of course upper case > > CPU models would still need to be accepted for backwards > > compatibility reasons. > > > > Note that I'm suggesting we adopt this approach consistently for all > > CPU models, including existing ones. So power8 should be accepted, as > > should be POWER11. > > > > CC'ing Daniel and David, both of which have worked on ppc64 in the > > past and might be able to offer additional insights / historical > > context. > > > > It has to do with IBM marketing. > > POWER is an acronym (Performance Optimization With Enhanced RISC) and all > marketing material demanded that it was mentioned in full caps, e.g. POWER7, > POWER8, POWER9. The reason why libvirt kept using full caps in libvirt, even > after QEMU changed it to lower, was due to IBM marketing demands. IBM wanted > users to use the full caps name in the domain XML, which is/was the official > way > customers would interact with the virtualization stack.
AFAIK there has never been any IBM marketing request to the libvirt project in respect of CPU names. Perhaps that was communicated to IBM contributors writing patches in private, but from POV of the libvirt community upstream that is irrelevant. We review patches based on their technical characteristics and AFAIR at the time QEMU became case insensitive, libvirt decided to stick with uppercase names, driven by the historical precedent that we had already established with earlier versions of libvirt. > In power10 it seems like IBM marketing changed its mind [1] and now the model > name is camel case, so now we're supposed to call them Power10, Power11, etc. This is the prime example of why marketing should be ignored when making technical decisions. They will always change their minds every few years. > Ignoring case seems a sensible change to make since we do not want > to be hostage of IBM marketing whims. I'm not sure we have any significant precedent of ignoring the case of user specified input. The general goal of libvirt XML input is to specify the data in a single canonical format and avoid redundant ways to specifying the same thing. IMHO we have two options - continue to use uppercase in all ppc CPU models, or switch to lowercase only for new CPU models we add. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
