Re: 2.6.25-rc5-git6: Reported regressions from 2.6.24

[Thomas Gleixner]

On Fri, 21 Mar 2008, Gabriel C wrote:
> > So the rotating watchdog triggers for a yet to figure out reason.
> > 
> > Oh, now that the pm timer seems to work again, can you try the following:
> > 
> > apply the reverted patch again and let the box boot. At some point the
> > TSC is marked unstable and is replaced by acpi_pm clocksource.
> > 
> > What result does timewarp.c show in that situation ?
> 
> Here it is , same kernel + Andi's patch :
> 
> ./time-warp-test
> 4 CPUs, running 4 parallel test-tasks.
> checking for time-warps via:
> - read time stamp counter (RDTSC) instruction (cycle resolution)
> - gettimeofday (TOD) syscall (usec resolution)
> - clock_gettime(CLOCK_MONOTONIC) syscall (nsec resolution)
> 
> | 1.78 us, TSC-warps:0 | 19.27 us, TOD-warps:0 | 19.37 us, CLOCK-warps:0

Ok. So the watchdog trigger is a false positive. 

Thinking more about it, it looks like Andi's change triggers some
hidden bug in the combination of NO_HZ and add_timer_on(), where the
CPU on which the timer is added is likely in a long idle sleep. I look
into this tomorrow.

Thanks for testing

       tglx
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