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    SubjectRe: PREEMPT_RT vs ADEOS: the numbers, part 1
    On Sun, Jun 12, 2005 at 10:59:02PM +0200, Ingo Molnar wrote:
    > if you want to measure hw-interrupt delays then under PREEMPT_RT you'll
    > need to use an SA_NODELAY interrupt handler. (which is a PREEMPT_RT
    > specific flag) If you use normal request_irq() or some parport driver
    > then the driver function will run in an interrupt thread and what you
    > are measuring is not interrupt latency but rescheduling latency.

    Karim, just in case you're not very familiar with parport, this should
    do the trick:

    diff --git a/drivers/parport/parport_pc.c b/drivers/parport/parport_pc.c
    --- a/drivers/parport/parport_pc.c
    +++ b/drivers/parport/parport_pc.c
    @@ -2286,7 +2286,7 @@ struct parport *parport_pc_probe_port (u
    }
    if (p->irq != PARPORT_IRQ_NONE) {
    if (request_irq (p->irq, parport_pc_interrupt,
    - 0, p->name, p)) {
    + SA_NODELAY, p->name, p)) {
    printk (KERN_WARNING "%s: irq %d in use, "
    "resorting to polled operation\n",
    p->name, p->irq);
    Unless I'm missing something, this mode is only valid if coding the RT
    code in the hardirq handler, which didn't seem the main benefit of
    preempt-RT to me, but it's still an interesting basic benchmark,
    especially now that local_irq_disable is "soft".

    But I'd be nice to also measure the performance of the non-RT part of
    the workload, just a suggestion if you have time.

    With above patch applied my crystal ball expects preempt-RT to perform
    much closer to adeos, but with the difference that the non-RT part of
    the system will still get the burden of the added complexity that adeos
    won't have.

    Thanks.
    -
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