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Re: [TAPSETS] Linux Kernel Event Trace Tool


* Guanglei Li (guanglei@cn.ibm.com) wrote:
> >If the person is interested into tracing the whole system (process 
> >events,
> >softirqs, interrupts and NMI) to see the root of a problem, then a 
> >"event lost"
> >will happen as soon as an NMI tries to reenter into the logging 
> >code. That will
> >leave an incomplete trace.
> >
> > Mathieu Desnoyers <compudj@krystal.dyndns.org>
> 
> >FChE
> >Not exactly.  Those functions could still in theory be instrumented,
> >but an actual run-time reentry into the probing system would be
> >detected, the probe short-circuited, and a "missed probe" would be
> >recorded.
> 
> So how about using semaphore in probe handler or spin lock in 
> _stp_sprintf. So that no event will be lost. The current 
> implementation will just abandon the processing of a probe handler if 
> there's already another probe handler running, even on a different 
> CPU.
> 

Semaphore and spin locks needs to explicitely disable interrupts to insure
no deadlock occurs when a resource is shared with interrupt handlers.

NMIs, by nature, cannot be disabled.


Mathieu

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