On Monday, 14 August 2017 11:46:42 PDT Willem de Bruijn wrote: > > By the way, what were the usecases for the peek offset feature? > > The idea was to be able to peek at application headers of upper > layer protocols and multiplex messages among threads. It proved > so complex even for UDP that we did not attempt the same feature > for TCP. Also, KCM implements demultiplexing using eBPF today.
Interesting, but how would userspace coordinate like that? Suppose multiple threads are woken up by a datagram being received, they peek at a certain offset shared among them all to see which one reads. Suppose that thread is slow or blocked and, while it's getting its act together, another datagram arrives. Because of that, the other threads can't disable their polling. They will continually be woken up by the kernel if they go back to poll/select. Even with epoll, there's no new edge trigger since event is already at level. How will they avoid busy-waiting? And won't this secondary coordination obviate the need for offset peeking? -- Thiago Macieira - thiago.macieira (AT) intel.com Software Architect - Intel Open Source Technology Center
