Re: latest 'guaranteed low latency' patch against 2.2.14

[Kevin Morgan]

MontaVista certainly won't recreate the work of Ingo!  That is nice work.
However, preemption points have their limitations, and are difficult to
maintain over time.  Also, preemption points don't address excessive
interrupt off paths (which are significant and already reported as problems
from more than one of our customers).  We are doing general characterization
work now (with an immediate focus on our customer reported responsiveness
problems), and will also do these characterizations on systems with Ingo's
patches; we'll report the results here and on our web pages.   Preliminary
data indicates there is plenty of opportunity for dramatic response
characteristic improvements in Linux, and we believe those opportunities
extend well beyond what is achieveable with carefully placed preemption
points.   Our initial data on this will be forthcoming, and will flow out
over time as we work through a sequence of improvement efforts.

-Kevin Morgan
  VP Engineering, MontaVista

ps: yes all MontaVista product work in kernel space will of course be
released under GPL, just as our compact PCI
backplane networking and powerPC cross development packages have been
released under GPL.

pps: We have no illusions about getting native Linux down the the RTLinux
range of responsiveness, 15-20 microsecond "guaranteed" kinds of levels.
RTLinux is a fine solution for that level of real-time requirement.

Ingo Molnar wrote:

> On Sun, 6 Feb 2000, Benno Senoner wrote:
>
> >    Building upon a "one hundred percent pure Linux" base, MontaVista is
> >    characterizing driver-level and user process response
> >    characteristics in the
> >    Linux kernel and engineering a range of improvements to enable
> >    guaranteed
> >    single-millisecond response times. All such enhancements will be
> >    released back to the open source community under the Gnu Public
> >    License.
>
> all and any GPL-ed kernel enhancements are welcome of course. Currently
> with the lowlatency patch i cannot see bigger latencies than 500
> microseconds on my system (under heavy load), so we have better than
> 'single-millisec latencies'.
>
> you can find the latest lowlatency patch against 2.2.14 at:
>
>         http://www.redhat.com/~mingo/lowlatency-2.2.14-B1
>
> -- mingo
>
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