On Wed, 2019-05-15 at 13:54 +0200, Andrew Jones wrote: > On Wed, May 15, 2019 at 12:52:29PM +0200, Igor Mammedov wrote: > > since using magic numbers is not very descriptive > > (but if there is some spec where they come from that we could point users to > > it might be acceptable too, but I'd reserve number approach for values > > only). > > The numbers aren't magic, they're part of the name. '1' in the above > 'sve1' means one quadword. It would probably have been better to use bits > instead in the example, i.e. > > -cpu host,sve128=on,sve256=on,sve384=off,sve512=on > > where it's now clear that "sve512" has an analogy with x86's "avx512". > [...] > > So I set off to convince Igor of the wide word idea (he sits next to me, > so I didn't have go far), but he has convinced me of the above property > idea. He used the magic phrase: "less code would be needed". If we use > the properties like above then we get introspection for free (cpu property > listing which libvirt already knows how to do) - so no QMP query needed. > The cost is adding several properties (16 to handle the current 2048-bit > limit), but I guess that's cheap enough. The command line is verbose, but > also much easier for a human to construct and read. I'm pretty sold on > this path, but adding Andrea and Eduardo for their input as well.
Sorry for taking a while to respond. Anyway, the above looks good to me as a general direction, but note that you'll have to implement at the very least the query-cpu-model-expansion QMP command for the introspection to work. query-cpu-model-baseline and query-cpu-model-comparison are two more QMP command which, while perhaps not immediately applicabile, we will want to implement at some point; more in general, what s390x is doing with respect to CPU models is a good blueprint, according to the libvirt developer who's the most involved with that specific area of the project. -- Andrea Bolognani / Red Hat / Virtualization
