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    SubjectRe: latest 'guaranteed low latency' patch against 2.2.14
    On Tue, Feb 08, 2000 at 10:32:01PM +0100, Ingo Molnar wrote:
    > yep, completely agreed. Nevertheless there is a new method you might not
    > have heard about: the IOAPIC-based NMI watchdog i developed about a year
    > ago and which got added recently to the 2.3 SMP code. The NMI watchdog
    > also provides easy access to microsecond-resolution excuted (kernel level)
    > code - on standard PC (SMP) hardware. No kernel change is necessery, it's
    > part of the standard kernel. NMI interrupts are the 'secret backdoor' to
    > the PC architecture to guarantee hard-RT-latencies, even if the OS does
    > not directly support low latencies.
    >
    > any device interrupt can be turned into an NMI interrupt - of course
    > special handlers have to be written, and careful coding is needed as no
    > other kernel facilities can be relied on.


    This is an intrinsically terrible idea
    1. It creates drivers that are x86+IOAPIC specific
    2. It creates bizzare kernel bugs that will be impossible to track
    3. It creates a disgusting overhead in figuring out what nmi corresponds to what
    irq.
    4. It will make drivers fail with RTLinux . Of course they will be idiotic
    drivers, but ...



    >
    > -- mingo
    >
    >
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