I suspect not too many. It's a good bit of fiddling, and the benefits will be much less for WebSockets where the data is necessarily going to flow through userland. NIC TLS will save a bit of CPU, but it's not the big win you get with sendfile where you can avoid loading data from ram into registers, ciphering it, and writing it into (different) ram before DMA to the NIC; if you're high traffic mostly static files, you end up memory bandwidth limited, so saving a read and a write helps alot.