sched_userret priority adjustment patch for sched_4bsd

From: Stephan Uphoff (ups_at_tree.com)
Date: 09/25/04

  • Next message: Stephan Uphoff: "Re: scheduler (sched_4bsd) questions" 
    To: "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org>
Date: Sat, 25 Sep 2004 13:29:14 -0400

    When a thread is about to return to user space it resets its priority to
    the user level priority.
    However after lowering the permission its priority it needs to check if
    its priority is still better than all other runable threads.
    This is currently not implemented.
    Without the check the thread can block kernel or user threads with
    better priority until a switch is forced by by an interrupt.

    The attached patch checks the relevant runqueues and threads without
    slots in the same ksegrp and forces a thread switch if the currently
    running thread is no longer the best thread to run after it changed its
    priority.

    The patch should improve interactive response under heavy load somewhat.
    It needs a lot of testing.

            Stephan

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