On Tue, 11 Feb 2014, Andy Lutomirski wrote: Just adding Peter for now, as I'm too tired to grok the issue right now.
> Rumor has it that Linux 3.13 was supposed to get rid of all the silly > rescheduling interrupts. It doesn't, although it does seem to have > improved the situation. > > A small number of reschedule interrupts appear to be due to a race: > both resched_task and wake_up_idle_cpu do, essentially: > > set_tsk_need_resched(t); > smb_mb(); > if (!tsk_is_polling(t)) > smp_send_reschedule(cpu); > > The problem is that set_tsk_need_resched wakes the CPU and, if the CPU > is too quick (which isn't surprising if it was in C0 or C1), then it > could *clear* TS_POLLING before tsk_is_polling is read. > > Is there a good reason that TIF_NEED_RESCHED is in thread->flags and > TS_POLLING is in thread->status? Couldn't both of these be in the > same field in something like struct rq? That would allow a real > atomic op here. > > The more serious issue is that AFAICS default_wake_function is > completely missing the polling check. It goes through > ttwu_queue_remote, which unconditionally sends an interrupt. > > --Andy > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
