Subject: Re: [linux-audio-dev] Re: new preemptive kernel-patch from Montavista available
From: Roger Larsson (roger.larsson_AT_norran.net)
Date: Thu Nov 23 2000 - 22:53:13 EET
On Thursday 23 November 2000 20:39, yodaiken_AT_fsmlabs.com wrote:
> On Thu, Nov 23, 2000 at 10:17:25AM -0800, Nigel Gamble wrote:
> > My work is definitely a work in progress and proof of concept targetted
> > towards 2.5. I want to show that these techniques, which have been used
> > successfully in at least two previous versions of real-time unix,
> > REAL/IX from MODCOMP and IRIX from SGI, are easily applicable to Linux,
> > also.
>
> It's amazing how two people can look at the same thing and see something
> completely different. I look at REAL/IX and IRIX and see them as definitive
> proof that this technique is a total disaster. Both operating systems
> bloated into impossible to maintain, buggy, slow, disasters that needed
> specialized and very expensive hardware to provide unimpressive RT.
>
> MODCOMP's marketing claims 100microseconds worst case from interrupt to
> driver activation (not process activation) and "typical" "in the 50
> microsecond range on a 133 MHz Pentium based system" (not clear whether
> this is a off-the-shelf or MODCOMP hardware). Ordinary Linux give "typical"
> under 10 microseconds. Why is Linux performance so much better than the
> _marketing numbers_ for REAL/IX ? And I am willing to bet that Linux
> performance on real applications is stunningly better. Reason: this
> "succesful" technique imposes a huge cost that no amount of engineering
> effort can overcome.
>
> Benno: would you like a version of your benchmark that uses the RTLinux
> realtime from user space signal handlers ? Cort's been looking at it, and
> he thinks the major change needed will be to get around your adjustment for
> Linux usleep(20000) sleeps for 30ms.
I would be very interested at least.
/RogerL
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