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Bug#603229: Further information



On Tue, 2010-11-23 at 13:17 +0100, Frede Feuerstein wrote:
> Hi !
> 
> > This shows something about what's going wrong.  Could you please try
> > adding 'debug' to the kernel parameters?  That will show some more
> > context for these errors.
> 
> I booted 2.6.32-5 with the debug option on, and for comparison did the
> same with 2.6.30-2.
> 
> The errors concerning the power management itself are also showing up in
> 2.6.30-2.

The error message about 'domain->cpu_power' does not refer to power
management, but to the scheduler's estimation of the processing power of
each group of processor threads.

The scheduler is trying to group the processor threads by:

- NUMA node (NODE; sharing a connection to RAM)
- Package (CPU; sharing some caches)
- Core (MC; sharing execution units)

so that it can make good decisions about where a task should run when it
is ready to do so.

> But whereas 2.6.32-5 afterwards crashes with a divide error,
> 2.6.30-2 starts up normally:
[...]
> I suppose that it is the divide error in [0.852154], we have to deal
> with.
[...]

The division by zero appears to be a result of getting bad information
from the firmware about the groups of processors.  I realise that this
same bad information did not previously result in a crash, but I (and
the upstream developers) need to know what that information is before we
can understand how this can be avoided.

Ben.

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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