Messages in this thread | | | Date | Mon, 11 Jul 2005 16:12:37 +0100 (WEST) | Subject | Re: realtime-preempt-2.6.12-final-V0.7.51-11 glitches [no more] | From | "Rui Nuno Capela" <> |
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> * Rui Nuno Capela <rncbc@rncbc.org> wrote: > >> OTOH, I'll take this chance to show you something that is annoying me >> for quite some time. Just look to the attached chart where I've marked >> the spot with an arrow and a question mark. Its just one example of a >> strange behavior/phenomenon while running the jack_test4.2 test on >> PREEMPT_RT kernels: the CPU usage, which stays normally around 50%, >> suddenly jumps to 60% steady, starting at random points in time but >> always some time after the test has been started. Note that this >> randomness surely adds to the the slight differences found on the >> above results. > > how long does this condition persist? Firstly, please upgrade to the > -51-16 kernel, previous kernels had a condition where interrupt storms > (or repeat interrupts) could occur. (Your irqs/sec values dont suggest > such a condition, but it could still occur.) > > Then could you enable profiling (CONFIG_PROFILING=y and profile=1 boot > parameter), and create a script like this to capture a kernel profile > for a fixed amount of time: > > #!/bin/bash > > readprofile -r # reset profile > sleep 10 > readprofile -n -m /home/mingo/System.map | sort -n > > and start it manually when the anomaly triggers. Also start it during a > 'normal' period of the test. The output should give us a rough idea of > what is happening. This type of profiling is very low-overhead so it > wont disturb the condition. > > Note that you can increase the frequency and the quality of profiling by > enabling the NMI watchdog (LOCAL_APIC in the .config and nmi_watchdog=2 > boot option), in the -RT kernel it will automatically switch the > profiling tick to occur from NMI context. Such tracing will also show > overhead occuring in irqs-off functions. >
After several trials, with CONFIG_PROFILING=y and profile=1 nmi_watchdog=2 as boot parameters, I'm almost convinced I'm doing something wrong :)
- `readprofile` always just outputs one line:
0 total 0.0000
- `readprofile -a` gives the whole kernel symbol list, all with zero times.
Is there anything else I can check around here? -- rncbc aka Rui Nuno Capela rncbc@rncbc.org
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