HI Daniel,
Isn't the only scenario where another cpu can put an idle task on our runqueue, in nohz_idle_balance() where only the cpus in the nohz.idle_cpus_mask are iterated through. But for the case that this patch is addressing, the cpu in question is not yet a part of the nohz.idle_cpus_mask right?
Any other case would trigger load balancing on the same cpu, but we are preempt_disabled and interrupt disabled at this point.
Thanks
Regards Preeti U Murthy
On Fri, Feb 7, 2014 at 4:40 AM, Daniel Lezcano daniel.lezcano@linaro.org 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.
Cc: alex.shi@linaro.org Cc: peterz@infradead.org Cc: mingo@kernel.org Signed-off-by: Daniel Lezcano daniel.lezcano@linaro.org Signed-off-by: Peter Zijlstra peterz@infradead.org
kernel/sched/fair.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 428bc9d..5ebc681 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6589,6 +6589,13 @@ void idle_balance(struct rq *this_rq)
raw_spin_lock(&this_rq->lock);
/** While browsing the domains, we released the rq lock.* A task could have be enqueued in the meantime*/if (this_rq->nr_running && !pulled_task)return;if (pulled_task || time_after(jiffies, this_rq->next_balance)) { /* * We are going idle. next_balance may be set based on-- 1.7.9.5
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