On Mon, Jul 30, 2007 at 10:45:19AM +0100, Maciej W. Rozycki wrote: > On Sat, 28 Jul 2007, Russell King wrote: > > > Essentially, any complex interrupt handler (such as an IDE interrupt > > doing a multi-sector PIO transfer _in interrupt context_) can cause this > > kind of starvation. That's why Linux 1.x had bottom halves - so that > > the time consuming work could be moved out of the interrupt handler, > > thereby causing minimal the blockage of other interrupts. > > > > Unfortunately, that kind of design has been long since forgotten. > > Apparantly modern machines are fast enough that it doesn't have to be > > worried about anymore... Or are they? > > I would guess it is not that the machines are fast enough, but that this > two-level processing makes things more complicated. Enough that most > people would not bother digging into it unless really forced. Only > occasional latency problems are probably not enough of a force.
It's a shame we don't have a way to measure IRQ latency - it would be very useful to flag up problems. I think the best we could do is to arrange for the timer interrupt to complain if it's delayed by more than 1ms or so - but some architectures already run their timers with IRQF_DISABLED as a work around some of the latency issues. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
