• Gregory Haskins's avatar
    sched: pre-route RT tasks on wakeup · 318e0893
    Gregory Haskins authored
    In the original patch series that Steven Rostedt and I worked on together,
    we both took different approaches to low-priority wakeup path.  I utilized
    "pre-routing" (push the task away to a less important RQ before activating)
    approach, while Steve utilized a "post-routing" approach.  The advantage of
    my approach is that you avoid the overhead of a wasted activate/deactivate
    cycle and peripherally related burdens.  The advantage of Steve's method is
    that it neatly solves an issue preventing a "pull" optimization from being
    deployed.
    
    In the end, we ended up deploying Steve's idea.  But it later dawned on me
    that we could get the best of both worlds by deploying both ideas together,
    albeit slightly modified.
    
    The idea is simple:  Use a "light-weight" lookup for pre-routing, since we
    only need to approximate a good home for the task.  And we also retain the
    post-routing push logic to clean up any inaccuracies caused by a condition
    of "priority mistargeting" caused by the lightweight lookup.  Most of the
    time, the pre-routing should work and yield lower overhead.  In the cases
    where it doesnt, the post-router will bat cleanup.
    Signed-off-by: default avatarGregory Haskins <ghaskins@novell.com>
    Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    318e0893
sched_rt.c 16.6 KB