Re: [PATCH 2/7] sched: Add NEED_RESCHED to the preempt_count

From: Andy Lutomirski
Date: Tue Sep 10 2013 - 22:00:07 EST


On 09/10/2013 06:08 AM, Peter Zijlstra wrote:
> In order to combine the preemption and need_resched test we need to
> fold the need_resched information into the preempt_count value.
>
> We keep the existing TIF_NEED_RESCHED infrastructure in place but at 3
> sites test it and fold its value into preempt_count; namely:
>
> - resched_task() when setting TIF_NEED_RESCHED on the current task
> - scheduler_ipi() when resched_task() sets TIF_NEED_RESCHED on a
> remote task it follows it up with a reschedule IPI
> and we can modify the cpu local preempt_count from
> there.
> - cpu_idle_loop() for when resched_task() found tsk_is_polling().


It looks like the intel_idle code can get confused if TIF_NEED_RESCHED
is set but the preempt resched bit is not -- the need_resched call
between monitor and mwait won't notice TIF_NEED_RESCHED.

Is this condition possible?

--Andy

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