sched/rt: Prevent idle task boosting
Commit-ID: 1c4dd99bed5f6f70932bf8dacdd54d04a2619778 Gitweb: http://git.kernel.org/tip/1c4dd99bed5f6f70932bf8dacdd54d04a2619778 Author: Thomas Gleixner <[email protected]> AuthorDate: Mon, 6 Jun 2011 20:07:38 +0200 Committer: Ingo Molnar <[email protected]> CommitDate: Thu, 1 Mar 2012 10:28:05 +0100
sched/rt: Prevent idle task boosting
Idle task boosting is a nono in general. There is one exception, when PREEMPT_RT and NOHZ is active:
The idle task calls get_next_timer_interrupt() and holds the timer wheel base->lock on the CPU and another CPU wants to access the timer (probably to cancel it). We can safely ignore the boosting request, as the idle CPU runs this code with interrupts disabled and will complete the lock protected section without being interrupted. So there is no real need to boost.
Signed-off-by Thomas Gleixner <[email protected]>
Acked-by Peter Zijlstra <[email protected]>
Signed-off-by Ingo Molnar <[email protected]>
--- kernel/sched/core.c | 21 +++++++++++++++++++-- 1 files changed, 19 insertions(+), 2 deletions(-)
kernel/sched/core.c +19 -2
@@ -3779,6 +3779,24 @@ void rt_mutex_setprio(struct task_struct *p, int prio) rq =__task_rq_lock (p); +/* +* Idle task boosting is a nono in general. There is one +* exception, when PREEMPT_RT and NOHZ is active: +* +* The idle task calls get_next_timer_interrupt() and holds +* the timer wheel base->lock on the CPU and another CPU wants +* to access the timer (probably to cancel it). We can safely +* ignore the boosting request, as the idle CPU runs this code +* with interrupts disabled and will complete the lock +* protected section without being interrupted. So there is no +* real need to boost. +*/ +if (unlikely (p == rq->idle)) { +WARN_ON (p != rq->curr); +WARN_ON (p->pi_blocked_on); + goto out_unlock; + } +trace_sched_pi_setprio (p, prio); oldprio = p->prio; prev_class = p->sched_class;
@@ -3802,11 +3820,10 @@ void rt_mutex_setprio(struct task_struct *p, int prio)enqueue_task (rq, p, oldprio < prio ?ENQUEUE_HEAD :0 );check_class_changed (rq, p, prev_class, oldprio); +out_unlock: __task_rq_unlock(rq); } -#endif -void set_user_nice (struct task_struct *p,long nice) {int old_prio, delta, on_rq;