CVSROOT: /cvs
Module name: src
Changes by: v...@cvs.openbsd.org 2021/11/11 21:34:23
Modified files:
sys/kern : kern_event.c sys_generic.c
sys/sys : event.h
Log message:
Keep knotes between poll/select systems calls
Reduce the time overhead of kqueue-based poll(2) and select(2) by
keeping knotes registered between the system calls. It is expected that
the set of monitored file descriptors is relatively unchanged between
consecutive iterations of these system calls. By keeping the knotes,
the system saves the effort of repeated knote unregistering and
re-registering.
To avoid receiving events from file descriptors that are no longer in
the monitored set, each poll/select knote is assigned an increasing
serial number. Every iteration of poll/select uses a previously unused
range of serials for its knotes. In the setup stage, kqueue_register()
updates the serials of any existing knotes in the currently monitored
set. Function kqueue_scan() delivers only the events whose serials are
recent enough; expired knotes are dropped. When the serial range is
about to wrap around, all the knotes in the kqueue backend are dropped.
This change is a space-time tradeoff. Memory usage is increased somewhat
because of the retained knotes. The increase is limited by the number
of open file descriptors and active threads.
Idea from DragonFly BSD, initial patch by mpi@, kqueue_scan()-based
approach by me.
Tested by anton@ and mpi@
OK mpi@
