Subject: Re: [linux-audio-dev] Re: new preemptive kernel-patch from Montavista available
From: yodaiken_AT_fsmlabs.com
Date: Thu Nov 23 2000 - 21:39:28 EET
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.
-- --------------------------------------------------------- Victor Yodaiken Finite State Machine Labs: The RTLinux Company. www.fsmlabs.com www.rtlinux.com
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