Re: Hang and Soft Lockup problems with generic time code

[john stultz <johnstul@us.ibm.com>]

On Fri, 2006-07-07 at 23:36 -0500, James Bottomley wrote:
> > Did you really mean jumps of 200 seconds? Hmmm. The issue Roman and I
> > have been looking into does occur when we lose a number of ticks and
> > that confuses the clocksource adjustment code. The fix we're working
> > on
> > corrects the adjustment confusion, but doesn't fix the lost ticks.
> > 
> > However 200 seconds of lost ticks sounds very off. Could the driver be
> > disabling interrupt for such a long period of time?
> 
> Well, what I was seeing was that 
> 
> clocksource_read(clock) - clock->cycle_last
> 
> is returning a value about 200 x clock->cycle_interval

That then would be ~200 ticks. Is this at HZ=1000 ? 

> According to the debugging printks I put into update_wall_time().  I was
> assuming this was caused by a jump in the TSC count, but I suppose it
> could also be cause by spurious alterations to cycle_last or other
> effects I haven't traced.

Since this issue effected both the TSC and ACPI PM timer, I'd more
likely suspect something is holding off the timer interrupt. This could
be some kernel code like a driver, or it could be something like an SMI
from the BIOS.

thanks
-john