Re: interrupt latency

Linus Torvalds (torvalds@transmeta.com)
Wed, 12 Aug 1998 00:35:16 -0700 (PDT)

On Wed, 12 Aug 1998, Chris Wedgwood wrote:
>
> With the offset of 32, things work as expected and I am able to
> `generate interrupts'. Cool bananas.
>
> It means the guts of what I wanted to do will now have to be done in
> the module which means the interrupt times are going to be ring 0 ->
> ring 0 -> ring 0, instead of ring 3 -> ring 0 -> ring3, are the
> timings likely to be vastly different?

Different? Yes. "Vastly different"? Probably not.

However, usually when people are interested in interrupt latency, they
aren't so much interested in how long an interrupt takes to dispatch, but
how long interrupts may be disabled by whatever code that needs to do some
critical region or whatever.

And that is never going to be tested by a software interrupt. The whole
point of that kind of interrupt latency is to see how quickly the OS can
respond to an _unexpected_ and asynchronous thing.

Linus

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