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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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