Jan Kiszka wrote: > Markus Franke wrote: >> Dear all, >> >> I am running some latency tests with irqbench/irqloop. I am wondering >> whether it would be possible to achieve better results when activating >> CONFIG_PREEMPT and CONFIG_PREEMPT_VOLUNTARILY during the kernel >> configuration and running irqloop in User Mode over this kernel? > > Nope. > >> Does it make any sense? > > Nope. :) > >> I think in theory it should give better results because >> this irqloop runs in secondary(linux) domain when started, right? An >> increasing preemptibility of the linux kernel should be better for the >> irqloop-task. > > The Linux kernel is already fully preemptible by Xenomai once you > applied the I-pipe patch. Therefore, you are free to pick the Linux > preemption strategy according to your *Linux* load, independent of what > the real-time part needs. > > Unless you have interactive Linux programs running, I can suggest to > pick PREEMPT_VOLUNTARILY or even PREEMPT_NONE, specifically on low-end > hardware. > >> All tests were made under heavy I/O and CPU load by means of "dd", >> "pingflood" and "cpuburn". Nevertheless, I can only achieve worse >> results when activating CONFIG_PREEMPT. > > Do you have CONFIG_DEBUG_PREEMPT set as well then? This option still as > a small but measurable impact on Xenomai due to micro-dependencies that > as scheduled to be removed in the near future.
Hmm, I should have better said "tiny". This experience is based on I-pipe tracer observations, and I guess you don't have that thing on, have you? How much is the difference? How long did you measure to exclude noise. Jan
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