Re: Anyone tracing interrupt enable/disable?

* VomLehn, David ([email protected]) wrote:
> I'm pretty new to LTT, so please forgive what may be an ignorant
> question, but is anyone tracing interrupt enable/disable events, such as
> local_irq_enable, local_irq_restore, etc.? This would seem to be very
> useful in certain circumstances, but might be tricky/performance
> critical enough to require a specialized function or set of functions.
> 

Hi,

Just enable the "Locking" facility in the kernel menuconfig,
Instrumentation section. Make sure that after issuing lttctl -R to stop
tracing, you check the dmesg output for events lost. Because of its very
high event throughput, you may need to increase buffer size (see lttctl
-h to see how).

The current implementation uses the kernel/lockdep.c irq tracer, which
might not be available to all platforms. (tested on x86 and x86_64)

Also, be aware that on x86_64, I have seen _very_ high irq
enable/disable event rate due to idle=poll kernel config option, because
its idle loop basically enable/disable interrupts all the time.

Mathieu

> --
> David VomLehn, Staff O/S Software Engineer
> Scientific Atlanta, A Cisco Company
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-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
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