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    SubjectRe: [PATCH 1/3] Separate IRQ-stacks from 4K-stacks option
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    On Fri, 2004-09-10 at 11:34, Arjan van de Ven wrote:
    > On Fri, Sep 10, 2004 at 05:28:52PM +0200, Andrea Arcangeli wrote:
    > > On Fri, Sep 10, 2004 at 05:15:38PM +0200, Arjan van de Ven wrote:
    > > > What we should consider regardless is disable the nesting of irqs for
    > > > performance reasons but that's an independent matter
    > >
    > > disabling nesting completely sounds a bit too aggressive, but limiting
    > > the nesting is probably a good idea.
    >
    > disabling is actually not a bad idea; hard irq handlers run for a very short
    > time

    The glaring exception is the IDE io completion, which can run for 2000+
    usec even with a modern chipset and drive. Here's a 600 usec trace:

    http://krustophenia.net/testresults.php?dataset=2.6.8-rc4-bk3-O7#/var/www/2.6.8-rc4-bk3-O7/ide_irq_latency_trace.txt

    The timer, RTC, and soundcard interrupts (among others) will not like
    being delayed this long. Ingo mentioned that this was not always done
    in hardirq context; presumaby the I/O completion was done in a softirq
    like SCSI. What was the motivation for moving such a long code path
    into the hard irq handler?

    Lee

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