From: Frederic Weisbecker check_preempt_wakeup() of fair class needs an uptodate sched clock value to update runtime stats of the current task. When a task is woken up, activate_task() is usually called right before ttwu_do_wakeup() unless the task is already in the runqueue. In this case we need to update the rq clock manually in case the CPU runs tickless because ttwu_do_wakeup() calls check_preempt_wakeup(). Signed-off-by: Frederic Weisbecker Cc: Alessio Igor Bogani Cc: Andrew Morton Cc: Avi Kivity Cc: Chris Metcalf Cc: Christoph Lameter Cc: Daniel Lezcano Cc: Geoff Levand Cc: Gilad Ben Yossef Cc: Hakan Akkan Cc: Ingo Molnar Cc: Kevin Hilman Cc: Max Krasnyansky Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Stephen Hemminger Cc: Steven Rostedt Cc: Sven-Thorsten Dietrich Cc: Thomas Gleixner --- kernel/sched/core.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f0fa54d..320abee 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1353,6 +1353,12 @@ static int ttwu_remote(struct task_struct *p, int wake_flags) rq = __task_rq_lock(p); if (p->on_rq) { + /* + * Ensure check_preempt_curr() won't deal with a stale value + * of rq clock if the CPU is tickless. BTW do we actually need + * check_preempt_curr() to be called here? + */ + update_nohz_rq_clock(rq); ttwu_do_wakeup(rq, p, wake_flags); ret = 1; } @@ -1530,8 +1536,17 @@ static void try_to_wake_up_local(struct task_struct *p) if (!(p->state & TASK_NORMAL)) goto out; - if (!p->on_rq) + if (!p->on_rq) { ttwu_activate(rq, p, ENQUEUE_WAKEUP); + } else { + /* + * Even if the task is on the runqueue we still + * need to ensure check_preempt_curr() won't + * deal with a stale rq clock value on a tickless + * CPU + */ + update_nohz_rq_clock(rq); + } ttwu_do_wakeup(rq, p, 0); ttwu_stat(p, smp_processor_id(), 0); -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/