Jeremy Fitzhardinge wrote:
The softlockup watchdog is currently a nuisance in a virtual machine, since the whole system could have the CPU stolen from it for a long period of time. While it would be unlikely for a guest domain to be denied timer interrupts for over 10s, it could happen and any softlockup message would be completely spurious.
No, it is not unlikely. 4-way SMP VMs idling exhibit this behavior with NO_HZ or NO_IDLE_HZ because they get quiet enough to schedule nothing on the APs.
And that can happen on native hardware as well.
Earlier I proposed that sched_clock() return time in unstolen nanoseconds, which is how Xen and VMI currently implement it. If the softlockup watchdog uses sched_clock() to measure time, it would automatically ignore stolen time, and therefore only report when the guest itself locked up. When running native, sched_clock() returns real-time nanoseconds, so the behaviour would be unchanged. Does this seem sound? Also, softlockup.c's use of jiffies seems archaic now. Should it be converted to use timers? Mightn't it report lockups just because there was no timer event?
This looks good to me, as a first order approximation. But on native hardware, with NO_HZ, this is just broken to begin with. Perhaps we should make SOFTLOCKUP depend on !NO_HZ.
Zach - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
