• Peter Zijlstra's avatar
    sched: backward looking buddy · 4793241b
    Peter Zijlstra authored
    Impact: improve/change/fix wakeup-buddy scheduling
    
    Currently we only have a forward looking buddy, that is, we prefer to
    schedule to the task we last woke up, under the presumption that its
    going to consume the data we just produced, and therefore will have
    cache hot benefits.
    
    This allows co-waking producer/consumer task pairs to run ahead of the
    pack for a little while, keeping their cache warm. Without this, we
    would interleave all pairs, utterly trashing the cache.
    
    This patch introduces a backward looking buddy, that is, suppose that
    in the above scenario, the consumer preempts the producer before it
    can go to sleep, we will therefore miss the wakeup from consumer to
    producer (its already running, after all), breaking the cycle and
    reverting to the cache-trashing interleaved schedule pattern.
    
    The backward buddy will try to schedule back to the task that woke us
    up in case the forward buddy is not available, under the assumption
    that the last task will be the one with the most cache hot task around
    barring current.
    
    This will basically allow a task to continue after it got preempted.
    
    In order to avoid starvation, we allow either buddy to get wakeup_gran
    ahead of the pack.
    Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Acked-by: default avatarMike Galbraith <efault@gmx.de>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    4793241b
sched_fair.c 40.6 KB