If some expert in this area can help I'd appreciate it. And I'll note immediately that the issue I'm looking into I've only investigated thoroughly with 2.6.29 vanilla. In 2.6.29 we added an NMI watchdog timer to sparc64, it operates identically to how the x86 one works except that it's on by default :-) When the qla2xxx driver is built into the kernel statically, the firmware load causes an NMI watchdog timeout. The qla2xxx driver is fine, it only actually disables interrupts for very short periods to program the chip registers, telling it to load a few blocks of the firmware via DMA or similar. Then it waits for the interrupt to signal the firmware partial-load is done using wait_for_completion_timeout() (see qla2x00_mailbox_command in drivers/scsi/qla2xx/qla_mbx.c) Assuming NOHZ is enabled, what if qla2xxx driver init is the only running task on a cpu, no timers (at least for 5 seconds, the NMI timeout) are due to fire, and the qla2xxx code loops in this manner for more than 5 seconds loading the firmware? As far as I can see it, the NOHZ code has no reason to start the timer firing again in this situation. So we'll just loop continuously into the scheduler (to wait for the qla2xxx driver completion). I believe the events trigger quick enough that need_resched() is not true if the scheduler even makes it to the idle thread. So the sequence seems to be scheduling in and out of a pure kernel thread, with no pending non-scheduler timers for a long time, and all this happening for longer than the NMI watchdog timeout, with NOHZ enabled. I'll note that adding printk's (this is a serial console) to the qla2xxx mailbox command code makes the NMI watchdog problem go away :) But if I only put printk's around the entire firmware loading sequence, the NMI watchdog does trigger. Is there something fundamental that should be preventing 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
