* Dave Martin (dave.mar...@arm.com) 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. > > 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.
SVE *is* a bit unusual. In most CPU features they're actually features, they're on or off, so we have a big list of features that are enabled/disabled. We've had that type of thing (at least on x86) for years and it's OK. We've got one or two things where they're numerical (e.g. host-physbits) and we struggle a bit with how to handle them. SVE is somewhere in between - it's a list of numbers, apparently a fairly large arbitrarily set of numbers that could be chosen so you'd need lots of feature flags (sve1...sve64 say or more); so that doesn't fit the existing things we've had that have worked. Dave > 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. > > Cheers > ---Dave -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
