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. > Hi all, > > Drew suggested this as an alternative approach to recording the ioctl > number on the vcpu struct [1] as it may benefit other architectures in > general. > > I had a look at some of the specific ioctls across architectures, but > must admit that I can't easily tell which architecture specific logic > relies on having registered preempt notifiers and having called the > architecture specific load function. > > It would be great if you would let me know if you think this is > generally useful or if you prefer the less invasive approach, and in > case this is useful, if you could have a look at all the vcpu ioctls for > your architecture and let me know if I am being too loose or too > careful in calling __vcpu_load() in this patch. I can suggest a third approach: if (ioctl == KVM_GET_ONE_REG || ioctl == KVM_SET_ONE_REG) return kvm_arch_vcpu_ioctl(filp, ioctl, arg); in kvm_vcpu_ioctl before "r = vcpu_load(vcpu);", or even better: if (ioctl == KVM_GET_ONE_REG) // call kvm_arch_vcpu_get_one_reg_ioctl(vcpu, ®); // and do copy_to_user return kvm_vcpu_get_one_reg_ioctl(vcpu, arg); if (ioctl == KVM_SET_ONE_REG) // do copy_from_user then call // kvm_arch_vcpu_set_one_reg_ioctl(vcpu, ®); return kvm_vcpu_set_one_reg_ioctl(vcpu, arg); so that the kvm_arch_vcpu_get/set_one_reg_ioctl functions are called without the lock. Then all architectures except ARM can be switched to do vcpu_load/vcpu_put in kvm_arch_vcpu_get/set_one_reg_ioctl Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html