On 8/8/07, Andi Kleen <[EMAIL PROTECTED]> wrote: > On Thursday 09 August 2007 01:17:19 Aaron Durbin wrote: > > In setup_APIC_timer with the HPET in use, a condition can arise while > > waiting for the next irq slice to expire on the HPET which will either > > cause an NMI watchdog to fire or a 3 minute busy loop if the NMI > > watchdog is disabled. > > > > The HPET comparator and the counter keep incrementing during its normal > > operation. When a comparison event fires the comparator will increment > > by the designated period. If the HPET trigger occurs right after > > the 'int trigger = hpet_readl(HPET_T0_CMP);' line, we will will spin > > for up to 3 minutes (with a clock of 25MHz) waiting for the HPET > > counter to wrap around. However, when the NMI watchdog is enabled the > > NMI watchdog will detect a lockup and reboot the machine. This > > scenario can be exasperated by the presence of an SMI which will > > increase the window of opportunity for the condition to occur. > > Nasty. > > Iirc the clockevents code did away with the synchronization > completely because Thomas determined it was useless because long term > it'll drift anyways. So perhaps it could be just removed? >
I was thinking along the same lines as well, but I really didn't know how important all that code was for waiting for the next irq slice. I'm not time expert, but I would imagine we would resynchronize correctly in the future after this code path? - 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/
