On Fri, Jan 17, 2014 at 10:04:02AM +0100, Daniel Lezcano wrote:
The scheduler main function 'schedule()' checks if there are no more tasks on the runqueue. Then it checks if a task should be pulled in the current runqueue in idle_balance() assuming it will go to idle otherwise.
But the idle_balance() releases the rq->lock in order to lookup in the sched domains and takes the lock again right after. That opens a window where another cpu may put a task in our runqueue, so we won't go to idle but we have filled the idle_stamp, thinking we will.
This patch closes the window by checking if the runqueue has been modified but without pulling a task after taking the lock again, so we won't go to idle right after in the __schedule() function.
Did you actually observe this or was it found by reading the code?