Peter Zijlstra <pet...@infradead.org> writes: > On Wed, Feb 15, 2017 at 10:34:58AM +0200, Alexander Shishkin wrote: > >> Well, we can't make the limitation go away. You'll still have to stop >> kvms to get any 'meaningful' PT data. > > Why would you need to stop all VMs in order to get your !VM data? Sure, > you get black holes where the VM runs, but we should be able to see > everything else.
No, what I mean is that if you run kvm prior to starting perf record, which I assume is the case for acme, your entire session is a black hole. The VMXON happens pretty early on, you can open /dev/kvm, ioctl(KVM_CREATE_VM) on it and that will do a VMXON already. The problem is that PT (on BDW) doesn't trace inside VM root mode, not just between VM entry/VM exit. Regards, -- Alex
