Markus Franke wrote: > Jan Kiszka wrote: >> Markus Franke wrote: >>> 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. :) >> 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. > > Well, "Native-API-Tour.pdf" states that everytime a mode switch from > Primary Domain to Secondary Domain is made (e.g. Linux system call like > ioctl()), Xenomai can ease from the > "continuous trend of improvements of Linux 2.6 regarding > preemptability". So CONFIG_PREEMPT should have an impact on measurements > with Xenomai, maybe not with irqbench/irqloop. The problem here is that > we don't have a mode switch, right? When running irqloop as User-Task it > simply runs in Secondary Mode, right?
Of course, irqloop runs in *primary* mode to be able to handle the events deterministically. So it is not directly affected by CONFIG_PREEMPT. Yes, if you have an RT thread that issues syscalls and wishes to have them handled as fast as possible, CONFIG_PREEMPT should be enabled (and CONFIG_XENO_OPT_RPIDISABLE should remain off, maybe you even want to consider CONFIG_XENO_OPT_ISHIELD then). Such RT application designs are tricky to get correct and deterministic, so it's often better to not rely on these properties and rather seek a clear separation of pure RT threads on the one side and Linux syscall issuing non-RT or RT borderline threads (low-prio RT threads that are being switched back and forth between primary and secondary mode) on the other. > >> 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. > > I cannot see anything like > > CONFIG_DEBUG_PREEMPT=y > or > #CONFIG_DEBUG_PREEMPT is not set > > in my config-file. The parameter simply doesn't exist. Shadowed by CONFIG_DEBUG=n likely. Jan _______________________________________________ Xenomai-help mailing list [email protected] https://mail.gna.org/listinfo/xenomai-help
