On 18/04/2017 16:16, Paolo Bonzini wrote: >> This patch allows userspace to tell how many VCPUs it is going to use, >> which can save memory when allocating the kvm->vcpus array. This will >> be done with a new KVM_CREATE_VM2 IOCTL. >> >> An alternative would be to redo kvm->vcpus as a list or protect the >> array with RCU. RCU is slower and a list is not even practical as >> kvm->vcpus are being used for index-based accesses. >> >> We could have an IOCTL that is called in between KVM_CREATE_VM and first >> KVM_CREATE_VCPU and sets the size of the vcpus array, but we'd be making >> one useless allocation. Knowing the desired number of VCPUs from the >> beginning is seems best for now. >> >> This patch also prepares generic code for architectures that will set >> KVM_CONFIGURABLE_MAX_VCPUS to a non-zero value. > Why is KVM_MAX_VCPU_ID or KVM_MAX_VCPUS not enough? Ok, for KVM_MAX_VCPUS I should have read the cover letter more carefully. :) Paolo
