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SubjectRe: a joint letter on low latency and Linux
Just for background: I am *not* a multimedia, audio, or anything like that  
guy. My most-used applications are gcc and a news/mail program (running
under dosemu, btw).

yodaiken@fsmlabs.com wrote on 01.07.00 in <20000701160143.A29436@hq.fsmlabs.com>:

> I don't know what a "specifically RT technique" is and I don't care
> how its done -- if the kernel can promise to always respond to an interrupt
> within some bound, then the kernel offers a hard realtime guarantee.
> And, for what it's worth, my professional opinion is that this is incredibly
> hard to do and never worth doing in a kernel that also wants to offer
> high speed networking, files systems, and guis.

FWIW, a kernel that cannot *at least* guarantee this will happen in
significantly more than 99% of the cases is broken for *every*
application.

According to the "hard real time" definitions given by, say, Larry,
*every* task is a hard real time task. There is *no* task that doesn't
have a deadline.

Those deadlines are of differing tightness (from microseconds to days) and
they are of differing importance - partly because the tasks themselves are
of differing importance, partly because the consequences of failure rates
differ. (And *everything* has failure rates. There is no perfect algorithm
in the real world.)

Oh, and 99% is a really crappy percentage. 1% of a year is nearly four
full days. 1% of a day is more than a full quarter hour. 1% of a 25*80
screen is 20 characters.

> I'm sure Ingo will tell you that his patch is designed to make long
> latencies _rare_ not impossible.

And that's exactly what is needed in the real world. IMO.

MfG Kai

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