On Wed, May 15, 2019 at 12:00:45PM +0100, Dave Martin wrote: > On Wed, May 15, 2019 at 09:18:54AM +0100, Andrew Jones wrote: > > On Tue, May 14, 2019 at 04:48:38PM +0200, Igor Mammedov wrote: > > > On Tue, 14 May 2019 11:02:25 +0200 > > > Andrew Jones <drjo...@redhat.com> wrote: > > > > My thought is primarily machines. If a human wants to use the command > > > > line and SVE, then I'm assuming they'll be happy with sve-max-vq or > > > > figuring out a map they like once and then sticking to it. > > > > > > maybe naive question, but why not use a property/bit as user facing > > > interface, > > > in line with what we do with CPUID bits. (that's assuming that bits have > > > fixed meaning). > > > Yes, it's verbose but follows current practice and works fine with -cpu > > > and > > > -device. > > > (I really hate custom preprocessing of -cpu and we were working hard to > > > remove > > > that in favor of canonical properties at the expense of more verbose CLI). > > > > > > > Are you asking if we should do something like the following? > > > > -cpu host,sve1=on,sve=2=on,sve3=off,sve4=on > > Note, there is nothing SVE-specific about this.
In the above example there is some specific SVE stuff there. If the command line has sve4=on, then it must also have sve1=on and sve2=on, per the architecture requiring all smaller power-of-2 vector lengths. Only sve3 is optional, but because it's optional we have to explicitly state when it's on or off in order to ensure we can cleanly fail a migration to a host that doesn't support that option. > > Either enabling features on a per-vcpu basis is justified, or it isn't: > if it's justified, then it would be better to have a general way of > specifying per-vcpu properties, rather than it being reinvented per > feature. > > Creating mismatched configurations is allowed by the architecture and so > it's useful for testing the kernel, but probably less useful for real- > world use cases today. > > So it may be a good idea to get the symmetric support sorted out first > before thinking about whether and how to specify asymmetric > configurations. These properties are per-vcpu for KVM only. QEMU doesn't have a way to allow per-vcpu features to be described on the command line yet. With '-cpu host,...' The '...' applies to all vcpus. So we are "just" working on the symmetric support now. Thanks, drew
