On Thu, Feb 08, 2024 at 08:13:26AM -0800, Andrea Bolognani wrote: > On Thu, Feb 08, 2024 at 03:54:20PM +0000, Daniel P. Berrangé wrote: > > On Thu, Feb 08, 2024 at 07:52:00AM -0800, Andrea Bolognani wrote: > > > > > That's fair, but I think it could still be useful to highlight that > > > > > the presence of the attribute in the *host* topology doesn't indicate > > > > > that attempting to use it in the *guest* topology will work, just to > > > > > avoid confusion. > > > > > > > > > > How about > > > > > > > > > > Note that this attribute is always present, even when the > > > > > architecture doesn't support guests with multiple CPU dies. > > > > > > > > The host topology info says nothing about what's possible in the > > > > guest. The only requirement for the guest is that QEMU is new > > > > enough to configure this. Aside from that any combo of sockets/ > > > > clusters/dies/cores/threads can be configured for the guest, > > > > regardless of what host topology reports. > > > > > > That's not correct. Even the latest version of QEMU only allows > > > configuring multiple dies and clusters for certain architectures. > > > > Yes but that's a constraint of the guest machine type choice, related > > to the host capabilities info. > > AFAICT there's no x86_64 (or ppc64, or s390x, or ...) machine type > that can use CPU clusters. I believe x86 should be gaining CPU cluster support in QEMU, though the current patch is suggesting to call them 'modules' when configuring the guest, just to absolutely maximise confusion when linux calls them 'clusters'. > So if you're planning to run a same-architecture VM (most common use > case) you are not going to be able to use CPU clusters, which might > be confusing considering that CPU clusters appear to be supported by > your host CPU according to the capabilities XML. On x86 AMD CPUs will report multiple dies while new Intel CPUs will report multiple clusters. In both cases, you'll be able to run a guest with multiple dies, if desire, and in future, with multiple clusters. 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 :| _______________________________________________ Devel mailing list -- devel@xxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxx
