On 23/11/2017 18:06, Christoffer Dall wrote: > On Thu, Nov 23, 2017 at 05:17:00PM +0100, Paolo Bonzini wrote: >> On 23/11/2017 17:05, Christoffer Dall wrote: >>> For example, >>> arm64 is about to do significant work in vcpu load/put when running a >>> vcpu, but not when doing things like KVM_SET_ONE_REG or >>> KVM_SET_MP_STATE. >> >> Out of curiosity, in what circumstances are these ioctls a hot path? >> Especially KVM_SET_MP_STATE. > > Perhaps my commit message was misleading; we only want to do that for > KVM_RUN, and not for anything else. We're already doing things like > potentially jumping to hyp mode and flushing VMIDs which really > shouldn't be done unless we actually plan on running a VCPU, and we're > going to do things like setting up the timer to handle timer interrupts > in an ISR, which doesn't make sense unless the VCPU is running. > > Add to that, that loading an entire VM's state onto hardware, only to > read back a single register from hardware and returning it to user > space, doesn't really fall within optimization vs. non-optimization in > the critical path, but is just wrong, IMHO. For GET/SET_ONE_REG it certainly makes sense. For everything else, I'm wondering which ioctls (and how many calls to each of them) exactly you are seeing, and also on which userspace paths. > That doesn't solve my need as I want to *only* do the arch vcpu_load for > KVM_RUN, I should have been more clear in the commit message. That's what you want to do, but it might not be what you need to do. Paolo
