Re: interrupt latency

Pavel Machek
2002-08-28T21:52:59Z

Hi!

> > On Tue, Aug 27, 2002 at 02:01:43PM -0400, Richard B. Johnson wrote:
> > > This cannot be. A stock kernel-2.4.18, running a 133 MHz AMD-SC520,
> > > (like a i586) with a 33 MHz bus, handles interrupts off IRQ7 (the lowest
> > > priority), from the 'printer port' at well over 75,000 per second without
> > > skipping a beat or missing an edge. This means that latency is at least
> > > as good as 1/57,000 sec = 0.013 microseconds.
> >
> > Assuming you mean 75,000 then ...
> > Thats 0.013 MILLISECONDS which is 13 microseconds and its not likely.
>
> Yes 13 microseconds.
>
> > I bet that your data source drops data or looks at some handshake
> > pins on the parallel connect.
> >
>
> No. You can easily read into memory 75,000 bytes per second from the
> parallel port, hell RS-232C will do 22,400++ bytes per second (224,000
> baud) on a Windows machine, done all the while to feed a PROM burner. I
> never measured Linux RS-232C, but it's got to be at least as good.

There's >16bytes FIFO at the rs-232, and kernel uses flip buffers so
that it does nlot have to wake userspace each time.

--
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