• Morten Rasmussen's avatar
    sched/fair: Add 'group_misfit_task' load-balance type · 3b1baa64
    Morten Rasmussen authored
    To maximize throughput in systems with asymmetric CPU capacities (e.g.
    ARM big.LITTLE) load-balancing has to consider task and CPU utilization
    as well as per-CPU compute capacity when load-balancing in addition to
    the current average load based load-balancing policy. Tasks with high
    utilization that are scheduled on a lower capacity CPU need to be
    identified and migrated to a higher capacity CPU if possible to maximize
    throughput.
    
    To implement this additional policy an additional group_type
    (load-balance scenario) is added: 'group_misfit_task'. This represents
    scenarios where a sched_group has one or more tasks that are not
    suitable for its per-CPU capacity. 'group_misfit_task' is only considered
    if the system is not overloaded or imbalanced ('group_imbalanced' or
    'group_overloaded').
    
    Identifying misfit tasks requires the rq lock to be held. To avoid
    taking remote rq locks to examine source sched_groups for misfit tasks,
    each CPU is responsible for tracking misfit tasks themselves and update
    the rq->misfit_task flag. This means checking task utilization when
    tasks are scheduled and on sched_tick.
    Signed-off-by: default avatarMorten Rasmussen <morten.rasmussen@arm.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: dietmar.eggemann@arm.com
    Cc: gaku.inami.xh@renesas.com
    Cc: valentin.schneider@arm.com
    Cc: vincent.guittot@linaro.org
    Link: http://lkml.kernel.org/r/1530699470-29808-3-git-send-email-morten.rasmussen@arm.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    3b1baa64
sched.h 57.9 KB