From: David Miller <davem@xxxxxxxxxxxxx> Date: Mon, 22 Jun 2009 02:27:52 -0700 (PDT) > I think something else is afoot, because while using "nohz=off" makes > the problem go away, simply adding a NMI watchdog touch after the > schedule() call in cpu_idle() does not make the problem go away. > > Also, the cpu that gets the NMI watchdog is different from the cpu > running the qla2xxx driver init. That basically destroys the bulk > of my theory :-) Ok, I think I know what's happening now. CPU 0 is in the driver init and looping submitting mailbox commands to load the firmware, then waiting for completion. CPU 1 is receiving the device interrupts. CPU 1 is where the NMI watchdog triggers. CPU 0 is submitting mailbox commands fast enough that by the time CPU 1 returns from the device interrupt handler, a new one is pending. This sequence runs for more than 5 seconds. The problematic case is CPU 1's timer interrupt running when the barrage of device interrupts begin. Then we have: timer interrupt return for softirq checking pending, thus enable interrupts qla2xxx interrupt return qla2xxx interrupt return ... 5+ seconds pass final qla2xxx interrupt for fw load return run timer softirq return At some point in the multi-second qla2xxx interrupt storm we trigger the NMI watchdog on CPU 1 from the NMI interrupt handler. The timer softirq, once we get back to running it, is smart enough to run the timer work enough times to make up for the missed timer interrupts. However, the NMI watchdogs (both x86 and sparc) use the timer interrupt count to notice the cpu is wedged. But in the above scenerio we'll receive only one such timer interrupt even if we last all the way back to running the timer softirq. I'm not exactly sure what to do about this. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
