About :: TODO :: Blog :: RSS :: Old blog :: Projects :: GIT :: Gallery :: Notes

Tue, 07 Nov 2006

I am ready new sick is kevent release.


No, I am sick and new kevent release is ready.
Actually not. Looking at how much I've eaten and how much I still want to eat, one can say that I'm definitely ok.

Nevertheless, new kevent release 'take23' is out.
There are several major changes in this release:

• new ring buffer implementation in process' memory. it works similar to this description, but structure has changed - I removed user's index, instead there is only kernel one (i.e. index where kernel will put new ready event). When user calls kevent_get_events() or kevent_wait() requested number of kevents is copied into ring buffer (if it was initialized using

  int kevent_ring_init(int ctl_fd, struct ring_buffer *ring, unsigned int num);

  function and kernel's index is increased. Simple. Userspace should itself store pointer to it's previous index (actually it can be calculated using returned value from kevent_wait() - it is number of events copied into ring buffer and current kernel's index, but it is only correct in case of special locking between threads.
• wakeup-one-thread flag. When several threads wait on the same kevent queue and requested the same event, for example 'wake me up when new client has connected, so I could call accept()', then all threads will be awakened when new client has connected, but only one of them can process the data. This problem is known as 'thundering nerd problem'. Events which have this flag set will not be marked as ready (and appropriate threads will not be awakened) if at least one event has been already marked.
• edge-triggered behaviour. It is an optimisation which allows to move ready and dequeued (i.e. copied to userspace) event to move into set of interest for given storage (socket, inode and so on) again. It is very usefull for cases when the same event should be used many times (like reading from pipe). It is similar to epoll()'s EPOLLET flag.

  epoll (no EPOLLET):                  57428 events/sec
  kevent (no ET):                      59794 events/sec
  epoll (with EPOLLET):                71000 events/sec
  kevent (with ET):                    78265 events/sec
  Maximum (busy loop reading events):  88482 events/sec

/devel/kevent :: Link / Comments (0)