[uClinux-dev] Interrupt latency on M5272

[Harry Gunnarsson]

Hi everybody,
I am running uClinux on a custom board with the following configuration
- 20070131 distro with 2.6.22.6 kernel
- M5272 CPU clocked at 60MHz (not 66..)
- Compiled with CodeSourcery 4.2-47
- Custom board has serial port, RJ45 ethernet

Essentially, our application only has one real-time requirement, everything
else is more of a control nature where there is no real time constraints.
The real-time event is served with an interrupt as
- Interrupt line hooked up to ext 3
- priority 5
- request_irq called with SA_INTERRUPT

We did some profiling on this interrupt and with a extremely stripped down
driver for the interrupt we see the following numbers
- 12.5 microsecond latency from interrupt line is pulled until service
routine is getting called.

If my arithmetic skills serve me right, that's 750 clock cycles.

Questions:
- Does this sound slow? Is this the latency you'd expect from a system
above?
- Does anyone else have any other interrupt performance stats for
ColdFire that he/she wants to share?
- Is there any way one can speed up the handling of an interrupt without
re-inventing linux?

Thanks in advance,
Harry
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