Philippe Gerum wrote: ... > Read my mail, without listening to your own grumble at the same time, > you should see that this is not a matter of being right or wrong, it is > a matter of who needs what, and how one will use Xenomai. Your grumble > does not prove anything unfortunately, otherwise everything would be > fixed since many moons.
Why things are unfixed has something to do with their complexity. RPI is a complex thing AND it is a separate mechanism to the core (that's why I was suggesting to reuse PI code if possible - something that is already integrated for many moons). > What I'm suggesting now, so that you can't tell the rest of the world > that I'm such an old and deaf cranky meatball, is that we do place RPI > under strict observation until the latest 2.4-rc is out, and we would > decide at this point whether we should change the default value for the > skins for which it makes sense (both for v2.3.x and 2.4). Obviously, > this would only make sense if key users actually give hell to the 2.4 > testing releases (Mathias, the world is watching you). OK, let's go through this another time, this time under the motto "get the locking right". As a start (and a help for myself), here comes an overview of the scheme the final version may expose - as long as there are separate locks: gatekeeper_thread / xnshadow_relax: rpilock, followed by nklock (while xnshadow_relax puts both under irqsave...) xnshadow_unmap: nklock, then rpilock nested xnshadow_start: rpilock, followed by nklock xnshadow_renice: nklock, then rpilock nested schedule_event: only rpilock setsched_event: nklock, followed by rpilock, followed by nklock again And then there is xnshadow_rpi_check which has to be fixed to: nklock, followed by rpilock (here was our lock-up bug) That's a scheme which /should/ be safe. Unfortunately, I see no way to get rid of the remaining nestings. And I still doubt we are gaining much by the lock split-up on SMP (it's pointless for UP due to xnshadow_relax). In case there is heavy migration activity on multiple cores/CPUs, we now regularly content for two locks in the hot paths instead of just the one everyone has to go through anyway. And while we obviously don't win a dime for the worst case, the average reduction of spinning times trades off against more atomic (cache-line bouncing) operations. Were you able to measure some improvement? Jan
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