Re: Why no interrupt priorities?

Arjan van de Ven
2004-02-27T07:14:56Z

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On Thu, Feb 26, 2004 at 02:21:34PM -0800, Mark Gross wrote:
> > hardware IRQ priorities are useless for the linux model. In linux, the
> > hardirq runs *very* briefly and then lets the softirq context do the
> > longer taking work. hardware irq priorities then don't matter really
> > because the hardirq's are hardly ever interrupted really, and when they
> > are they cause a performance *loss* due to cache trashing. The latency
> > added by waiting briefly is going to be really really short for any sane
> > hardware.
>
> Keep in mind the context is Linux running on non-sane hardware, sloooow CPUs,

50Mhz is already really really fast in this context.

> latency sensitive small io buffers etc. Losing system wide throughput to have
> the hardware codec not be starved is a happy trade off to make.

The point I tried to make was that it would INCREASE latency. Unless you
have misdesigned device drivers, which is something that is fixable :)

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