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    SubjectRe: hot cache line due to note_interrupt()
    Ravikiran G Thirumalai <kiran@in.ibm.com> wrote:
    >
    > On Mon, Nov 10, 2003 at 03:58:44PM -0600, Jack Steiner wrote:
    > >
    > > I dont know the background on note_interrupt() in arch/ia64/kernel/irq.c,
    > > but I had to disable the function on our large systems (IA64).
    > >
    > > The function updates a counter in the irq_desc_t table. An entry in this table
    > > is shared by all cpus that take a specific interrupt #. For most interrupt #'s,
    > > this is a problem but it is prohibitive for the timer tick on big systems.
    > >
    > > Updating the counter causes a cache line to be bounced between
    > > cpus at a rate of at least HZ*active_cpus. (The number of bus transactions
    >
    > The answer to this is probably alloc_percpu for the counters.

    Or just make noirqdebug the default.

    The note_interrupt() stuff is only useful for diagnosing mysterious lockups
    (and hasn't proven useful for that, actually). It should be disabled for
    production use.


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