Why printk() is so complicated (and how to fix it)

The virtio ring buffer is most frequently used as a ring of pointers to other buffers. This wreaks havoc with performance as the virtual machine monitor is constantly having to (re) map the pointed-to buffer addresses to host-physical from guest-physical. Just something to consider. The newer virtio spec has a good solution to this (anti) feature, but it is only recently in the mainline kernel, so most distributions still have to deal with what virtio calls indirect buffers. It's easy to overlook the performance impact of "indirect" memory access and function calls.