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

Excerpts from David Olofson's message of 2011-07-21 01:03:32 +0200:
> On Thursday 21 July 2011, at 00.36.55, Philipp Überbacher
> <hollunder@lavabit.com> 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?

I do wonder whether the occasional peaks are due to the mainboards or
the CPUs. At least in the wild mainboards seem to have a lot of
influence (hardware interrupts or however they're called).

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Received on Thu Jul 21 04:15:03 2011