Re: 2us Interrupt latency's for Linux 2.0.xx

Manoj Apte (manoj@ERC.MsState.Edu)
Wed, 2 Sep 1998 03:27:15 -0500 (CDT)

> > in a handler). I created my own fast handler registered at IRQ32 (
> > interrupt is generated by
> > the APIC timer on a Ppro 200) that gives me a latency of approx 2300
> > nanoseconds
>
> the APIC timer interrupt is a CPU-internal IRQ, and thus has lower
> latencies. It should have identical latencies to a software interrupt.
> (like your numbers show). I measured 500 cycles _total_ profiling
> interrupt cost. This makes it possible to run 100 thousand IRQs a second
> profiling on a 100MHz P5. (i've tried it. It's noticeable but it works)
>

Agreed.. but my question was about why i see periodic mega-latencies of
the order of 15us every 30 seconds or so. I want to track the source of
this, so that _if_ i can dsiable that probelm, I have a much more
predictable APIC interrupt latency.

> _external_ interrupts have much higher latencies. (especially as old
> XT-PIC interrupts halt the CPU for a considerable amount of time ... this
> is not the case with IO-APIC and inter-CPU interrupts.)
>
> -- mingo
>

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