cvs commit: src/sys/kern subr_sleepqueue.c

[John Baldwin]

jhb         2004-11-05 20:19:58 UTC

  FreeBSD src repository

  Modified files:
    sys/kern             subr_sleepqueue.c 
  Log:
  - Store threads on sleep queues in FIFO order rather than sorted by
    priority.  The sleep queues don't get updated when the priority of
    threads changes, so sleepq_signal() might not always wakeup the
    highest priority thread.  Updating the queues when thread priorities
    change cannot be easily done due to lock orders, so instead we do an
    O(n) walk of the queue for a sleepq_signal() operation instead of O(1).
    On the other hand, adding a thread to a sleep queue now goes from O(n)
    to O(1) so it ends up as an even tradeoff.  The correctness here with
    regards to priorities is actually fairly important.  msleep() gives
    interactive threads their priority "boost" after they are placed on the
    queue, but before this fix that "boost" wasn't used to determine the
    highest priority thread that sleepq_signal() awoke.
  - Fix up some comments.
  
  Inspired by:    ups, bde
  
  Revision  Changes    Path
  1.14      +19 -16    src/sys/kern/subr_sleepqueue.c