2.6.36-stable review patch. If anyone has any objections, please let us know.
------------------ From: Mike Galbraith <[email protected]> commit f26f9aff6aaf67e9a430d16c266f91b13a5bff64 upstream. idle_balance() drops/retakes rq->lock, leaving the previous task vulnerable to set_tsk_need_resched(). Clear it after we return from balancing instead, and in setup_thread_stack() as well, so no successfully descheduled or never scheduled task has it set. Need resched confused the skip_clock_update logic, which assumes that the next call to update_rq_clock() will come nearly immediately after being set. Make the optimization robust against the waking a sleeper before it sucessfully deschedules case by checking that the current task has not been dequeued before setting the flag, since it is that useless clock update we're trying to save, and clear unconditionally in schedule() proper instead of conditionally in put_prev_task(). Signed-off-by: Mike Galbraith <[email protected]> Reported-by: Bjoern B. Brandenburg <[email protected]> Tested-by: Yong Zhang <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> LKML-Reference: <[email protected]> Signed-off-by: Ingo Molnar <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/fork.c | 1 + kernel/sched.c | 6 +++--- 2 files changed, 4 insertions(+), 3 deletions(-) --- a/kernel/fork.c +++ b/kernel/fork.c @@ -272,6 +272,7 @@ static struct task_struct *dup_task_stru setup_thread_stack(tsk, orig); clear_user_return_notifier(tsk); + clear_tsk_need_resched(tsk); stackend = end_of_stack(tsk); *stackend = STACK_END_MAGIC; /* for overflow detection */ --- a/kernel/sched.c +++ b/kernel/sched.c @@ -566,7 +566,7 @@ void check_preempt_curr(struct rq *rq, s * A queue event has occurred, and we're going to schedule. In * this case, we can save a useless back to back clock update. */ - if (test_tsk_need_resched(p)) + if (rq->curr->se.on_rq && test_tsk_need_resched(rq->curr)) rq->skip_clock_update = 1; } @@ -3821,7 +3821,6 @@ static void put_prev_task(struct rq *rq, { if (prev->se.on_rq) update_rq_clock(rq); - rq->skip_clock_update = 0; prev->sched_class->put_prev_task(rq, prev); } @@ -3883,7 +3882,6 @@ need_resched_nonpreemptible: hrtick_clear(rq); raw_spin_lock_irq(&rq->lock); - clear_tsk_need_resched(prev); switch_count = &prev->nivcsw; if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) { @@ -3915,6 +3913,8 @@ need_resched_nonpreemptible: put_prev_task(rq, prev); next = pick_next_task(rq); + clear_tsk_need_resched(prev); + rq->skip_clock_update = 0; if (likely(prev != next)) { sched_info_switch(prev, next); _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
