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    SubjectRe: kernel-hacking-HOWTO: An lk primer seeks feedback
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    >>>>> "Werner" == Werner Almesberger <almesber@lrc.di.epfl.ch> writes:

    Werner> Paul Rusty Russell wrote:
    >> `This document describes the common routines, locking systems and
    >> general requirements for kernel code: its goal is to serve as a
    >> primer for Linux kernel development.'

    Werner> 5.2: you may want to
    Werner> discuss disable_irq, disable_irq_nosync, and enable_irq. On
    Werner> most (all?) architectures, they are reasonably inexpensive
    Werner> ways to block specific interrupts. (BTW, why don't we actually
    Werner> have some kind of interrupt blocking that doesn't go down to
    Werner> the interrupt controller hardware ? Is the PIC part considered
    Werner> to be cheap enough in all possible cases ?)

    Actually I think the discussion of disable_irq/enable_irq should say
    something along the lines of "don't use these, if you think you need
    them, think again, if you still think you need them, think again real
    hard".

    enable_irq/disable_irq are quite expensive and should not be used
    except for very special cases. I'd claim that 99.9% of the time people
    are better off disabling interrupts directly on the device (most sane
    hardware has a bit to disable it) or using spin locks.

    Jes

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