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    SubjectRe: User mode drivers: part 1, interrupt handling (patch for 2.6.11)
    On Mon, 14 Mar 2005 12:42:27 +1100, Peter Chubb
    <peterc@gelato.unsw.edu.au> wrote:
    > >>>>> "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.

    Please put some big comments warning people about adding SA_SHARED. I
    can easily see someone thinking that they are fixing a bug by adding
    it. I'd probably even write a paragraph about what will happen if
    SA_SHARED is added.

    >
    > 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*
    >


    --
    Jon Smirl
    jonsmirl@gmail.com
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