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SubjectRe: interrupt latency
I don't care your list so somebody take out my e-mail address.

On Mon, 10 Aug 1998, Richard B. Johnson wrote:

> On Mon, 10 Aug 1998, Larry McVoy wrote:
>
> > : >Are there and patches/utilities/anything to measure interrupt latency
> > : >under linux ?
> > :
> > : The easiest way to measure interrupt latency is with a signal generator
> > : and an oscilloscope. No software solution is likely to give good results.
> >
> > 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?
> >
>
> With the Intel machines, you can. You can generate a software interrupt.
> You have to make, perhaps, a dummy driver that operates in ring 0 (kernel
> mode).
>
> This device could acquire an interrupt (IRQ) from the kernel. It could
> also generate a software interrupt for the IRQ number (they are not the
> same). The device could measure the time from which it generated a
> software interrupt to the time its ISR was called by the kernel.
>
> This time would include all the software overhead, but not the hardware
> overhead (which should be very, very much smaller than the software
> overhead). The fact that the kernel will mask/ACK/unmask the hardware
> controller(s) will not hurt the execution of the software interrupt.
>
> Now, that said, since all interrupts are handled the same except for
> the very small interval for the cascade, you could just review the
> generated assembly and calculate the execution times which might
> be simpler than writing the dummy driver. Nevertheless, if the driver
> was ismod-ed, and you could talk to it via ioctls (some new device
> in /dev), you could have a useful tool. It might not be useful for
> very long because I doubt that you could remove much code or improve
> upon the interrupt handling very much.
>
> Cheers,
> Dick Johnson
> ***** FILE SYSTEM WAS MODIFIED *****
> Penguin : Linux version 2.1.115 on an i586 machine (66.15 BogoMips).
> Warning : It's hard to remain at the trailing edge of technology.
>
>
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