Hi Tobias, Some more questions (inline) Tobias Knutsson wrote:
2.6.25.8-rt7 and 2.6.25.8 On Mon, Aug 11, 2008 at 14:48, Gregory Haskins <ghaskins@xxxxxxxxxx> wrote:Tobias Knutsson wrote:Hello, I'm trying to do some initial benchmarking on a rt-kernel versus a vanilla kernel. On the rt the results are stable in between test runs using the following command: cyclictest -t 1 -p 80 -c 1 -n -i 10000 -l 10000
What architecture is this? And what do you see for ave/max in the cyclictest output on -rt (so we have a reference)
However, using the same command while running the vanilla kernel, I get very varying results. And I would completely understand if it was due to increased jitter. The thing is, the jitter is very low (0% load) but the average times varies from 600 us to 6500 us depending on when the test is initiated.
What are you considering "jitter" when you say it is very low? Are the 600-6500us values truly from the "ave" output of cyclictest, or are these an average of the "max" output?
I imagine this might have something to do with not having high res timers in the vanilla kernel.
I will defer to Thomas, but my understanding is that 2.6.25 vanilla should have HRT as an option (though I am not sure if you enabled it or not).
If that is what's causing my problems.
Cyclictest will report that it cannot access the HRT when it cannot find it (at least it does on my system, but I might have an older version running). Do you see any such warnings?
What is the best way of comparing the two kernels?
This is a pretty good way, as long as you have HRT in the vanilla kernel. Assuming for a second that you do, your results are showing you what I would expect to see for vanilla (600-6500us spikes).
HTH -Greg
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