[Xenomai] Low latency under stress, otherwise high latency

Philippe Gerum rpm at xenomai.org
Wed Feb 28 19:06:39 CET 2018

On 02/26/2018 10:34 PM, Julian Viereck wrote:
> Hi folks,
> after installing Xenomai 3.0.5/kernel 4.9.38 following [1] on our Dell
> Precision 5820 machine (Intel Xeon W-2145), there are high latencies
> when the system is at rest. When starting a stress test via `stress -v
> -c 8 -i 10 -d 8`, the latency goes down (see terminal output below).
> Usually I would assume the latency increases with higher load and not go
> down. Does someone has an idea where to start in debugging / fixing the
> high latencies? Note that the cores are in C0 state 100% of the time
> (with and without the load on the machine).

Maybe a SMI issue [1]. You may want to boot your hardware with a vanilla
kernel (unpatched, no Xenomai), then run the hwlatdetect test from the
rt testsuite [2]. If SMIs are detected, you may want to ask your BIOS
vendor to fix their code (some do actually).

[1] http://xenomai.org/2014/06/dealing-with-x86-smi-troubles/
[2] git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git


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