• Waiman Long's avatar
    sched/fair: Avoid redundant idle_cpu() call in update_sg_lb_stats() · a426f99c
    Waiman Long authored
    Part of the responsibility of the update_sg_lb_stats() function is to
    update the idle_cpus statistical counter in struct sg_lb_stats. This
    check is done by calling idle_cpu(). The idle_cpu() function, in
    turn, checks a number of fields within the run queue structure such
    as rq->curr and rq->nr_running.
    
    With the current layout of the run queue structure, rq->curr and
    rq->nr_running are in separate cachelines. The rq->curr variable is
    checked first followed by nr_running. As nr_running is also accessed
    by update_sg_lb_stats() earlier, it makes no sense to load another
    cacheline when nr_running is not 0 as idle_cpu() will always return
    false in this case.
    
    This patch eliminates this redundant cacheline load by checking the
    cached nr_running before calling idle_cpu().
    Signed-off-by: default avatarWaiman Long <Waiman.Long@hpe.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Douglas Hatch <doug.hatch@hpe.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Mike Galbraith <efault@gmx.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Scott J Norton <scott.norton@hpe.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/1448478580-26467-2-git-send-email-Waiman.Long@hpe.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    a426f99c
fair.c 221 KB