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    SubjectRe: User mode drivers: part 1, interrupt handling (patch for 2.6.11)
    >>>>> "Jon" == Jon Smirl <jonsmirl@gmail.com> writes:

    >> The scenario I'm thinking about with these patches are things like
    >> low-latency user-level networking between nodes in a cluster, where
    >> for good performance even with a kernel driver you don't want to
    >> share your interrupt line with anything else.

    Jon> The code needs to refuse to install if the IRQ line is shared.

    It does. The request_irq() call explicitly does not include SA_SHARED
    in its flags, so if the line is shared, it'll return an error to user
    space when the driver tries to open the file representing the interrupt.

    Jon> Also what about SMP, if you shut the IRQ off on one CPU isn't it
    Jon> still enabled on all of the others?

    Nope. disable_irq_nosync() talks to the interrupt controller, which
    is common to all the processors. The main problem is that it's slow,
    because it has to go off-chip.

    --
    Dr Peter Chubb http://www.gelato.unsw.edu.au peterc AT gelato.unsw.edu.au
    The technical we do immediately, the political takes *forever*
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