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SubjectRe: interrupt latency
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>I reall wish this wasn't the case because I would dearly love to be able to
>have interrupt latency as a benchmark test in lmbench. Are you sure there
>is no way to do this in software? What if you had some way to generate
>interrupts essentially continuously?

I can't think of any way it could be done, certainly not sufficiently portably
to be of use to you in lmbench. There are two components to the interrupt
latency that the hardware sees; firstly the latency inherent in the
interrupt-handling code (how long does it take to get in, service the IRQ and
get out again) and secondly the extra latency induced by IRQs having been
disabled at the instant the interrupt occurred.

The former might be measurable in software and is certainly an interesting
statistic in its own right, but for people interested in real-time work (or
even device drivers under some circumstances) the second measurement is
important also; possibly more so because it's a lot harder to put a bound on
it. And without using special hardware or instrumenting the kernel, I can't
think how you could measure this part.

p.



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