[$] A medley of performance-related BPF patches

One of the advantages of the in-kernel BPF virtual machine is that it isfast. BPF programs are just-in-time compiled and run directly by the CPU,so there is no interpreter overhead. For many of the intended use cases,though, "fast" can never be quite fast enough. It is thus unsurprisingthat there are currently anumber of patch sets under development that are intended to speed up oneaspect or another of using BPF in the system. A few, in particular, seemabout ready to hit the mainline.