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    SubjectRe: [PATCH] Tasklets: Avoid duplicating __tasklet_{,hi_}schedule() code
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    On Wed, Feb 20, 2008 at 11:41:13AM +0100, Ingo Molnar wrote:
    >
    > * Ahmed S. Darwish <darwish.07@gmail.com> wrote:
    >
    > > > > - local_irq_disable();
    > > > > - t->next = __get_cpu_var(tasklet_vec).list;
    > > > > - __get_cpu_var(tasklet_vec).list = t;
    > > > > - __raise_softirq_irqoff(TASKLET_SOFTIRQ);
    > > > > - local_irq_enable();
    > > > > + /* We were not lucky enough to run, reschedule. */
    > > > > + __tasklet_schedule(t);
    > > >
    > > > i think there's a subtle difference that you missed: this one does
    > > > __raise_softirq_irqoff(), while __tasklet_schedule() does a
    > > > raise_softirq_irqoff(). (note the lack of undescores)
    > > >
    > > > the reason is to avoid infinitely self-activating tasklets.
    > >
    > > Indeed, thanks a lot for the explanation. (maybe it's time to check
    > > for new eyeglasses ;)).
    >
    > nah, it's rather subtle and the code looked good to me at first but i
    > remembered that there was some small detail here to watch out for.
    >
    > i really dont like tasklets due to their many, arbitrary scheduling
    > limitations, we should really use the "turn tasklets into kthreads"
    > patch i posted last year.
    >

    While we are at it, there's a small question that is bothering me
    for a while (and I'm really thankful for help).

    I keep reading that softirqs (and naturally, tasklets) got executed
    in interrupt context at the return from hardirq code path.

    Checking entry_32.S, I find no mentioning of softirqs on the return
    path (beginning from ret_from_intr: to restore_all: )

    The only invocation I'm able to find is from local_bh_enable() and
    from ksoftirqd/n threads (by calling do_softirq()). AFAIK, both
    invocations occur in a _nont-interrupt_ context (exception context).

    So, where does the interrupt-context tasklets invocation really
    occur ?

    Thanks

    --
    Ahmed S. Darwish
    Homepage: http://darwish.07.googlepages.com
    Blog: http://darwish-07.blogspot.com



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