Cornelius Köpp wrote:
Hello,
I run the latency test from testsuite on several hard and software configurations. 
Running on Xenomai 2.4.2, Linux 2.6.24 the results shows a "strange" behavior: 
In Kernel mode (-t1) the latencys constantly linear decrease. See attached plot 
'drifting_latencys_in_kernelmode.png' of latency test running 48h on Pentium3 700. This 
effect could be reproduced, even on other hardware (Pentium-M 1400).


As our P3 boards did not support APIC-based timing (IIRC), your kernel has correctly disabled the related kernel support. But the Pentium M should be fine. So could you check if we are seeing some TSC clocks vs. PIT timer rounding issue by enabling the local APIC on the Pentium M?

The usermode (-t0) did not show a drifting, but is influenced by a test ran in 
kernelmode before.

What do you mean with "is influenced"?


I talked with Sebastian Smolorz about this and he builds his own independent 
kernel-config to check. He got the same drifting-effect with Xenomai 2.4.2 and 
Xenomai 2.4.3 running latency over several hours. His kernel-config ist 
attached as 'config-2.6.24-xenomai-2.4.3__ssm'.

Our kernel-configs are both based on a config used with Xenomai 2.3.4 and Linux 
2.6.20.15 without any drifting effects.

2.3.x did not incorporate the new TSC-to-ns conversion. Maybe it is not a PIC vs. APIC thing, but rather a rounding problem of larger TSC values (that naturally show up when the system runs for a longer time).

Jan

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