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 <[email protected]> Cc: Alessio Igor Bogani <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Chris Metcalf <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: Geoff Levand <[email protected]> Cc: Gilad Ben Yossef <[email protected]> Cc: Hakan Akkan <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Li Zhong <[email protected]> Cc: Namhyung Kim <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Paul Gortmaker <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Thomas Gleixner <[email protected]> --- kernel/sched/core.c | 17 ++++++++++++++++- 1 files changed, 16 insertions(+), 1 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 2fcbb03..3c1a806 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1346,6 +1346,12 @@ 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; } @@ -1523,8 +1529,17 @@ 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); -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
