Re: [LAD] realtime kernel based on linux-3.0-rc7

On Thursday 21 July 2011, at 00.36.55, Philipp Überbacher
<hollunder@email-addr-hidden> wrote:
[...]
> > ..and this latency plot is stunning:
> > https://www.osadl.org/Latency-plot-of-system-in-rack-4-slot.qa-latencyplo
> > t-r4s6.0.html?latencies=&showno=&slider=57
[...]
> The plot really does look stunning, strangly (?) not on other machines.
> https://www.osadl.org/Latency-plot-of-system-in-rack-4-slot.qa-latencyplot-
> r4s7.0.html
> https://www.osadl.org/Latency-plot-of-system-in-rack-4-slot.qa-latencyplot
> -r4s8.0.html
>
> No idea what those plots tell about real world usage. It's good to get
> another set of patches though.

In terms of worst case figures, these plots look a bit like what I've seen
with RT-Linux and RTAI on various hardware (PII/III workstations via Geode
SBCs through Intel Core based Celerons on industrial Mini-ITX boards), though
with "true" RT kernels, one tends to get a lot of very low latency points, and
only the occasional peak.

SBCs with lowpower CPUs (Geode and the like) tend to perform a lot worse than
"proper" laptop and desktop CPUs. Memory and/or cache bandwidth issues, maybe?

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//David Olofson - Consultant, Developer, Artist, Open Source Advocate
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