On Tue, 2011-02-08 at 14:11 +0100, Gilles Chanteperdrix wrote: > Philippe Gerum wrote: > > On Tue, 2011-02-08 at 13:51 +0100, Henri Roosen wrote: > >> On Tue, Feb 8, 2011 at 1:31 PM, Gilles Chanteperdrix > >> <[email protected]> wrote: > >>> Philippe Gerum wrote: > >>>> On Tue, 2011-02-08 at 13:16 +0100, Gilles Chanteperdrix wrote: > >>>>> I was not talking about the Xenomai case specifically, but since Henri > >>>>> would like to have the full signals implementation with Xenomai, this > >>>>> does a apply to Xenomai too. > >>>>> > >>>>> > >>>> I think we all agree that having a complete signal implementation for > >>>> Xenomai in pure rt mode won't happen overnight. So the point is now: how > >>>> could it be mimicked, at least for the most useful part. > >>>> > >>> My point is that whatever you do, a switch user-kernel, then kernel-user > >>> is not going to be lightweight, so avoiding it in the application in the > >>> first place may be a better idea. > >>> > >>> My aim with implementing complete signals was rather for things like > >>> timer_* and mq_notify, where the interface requires them, I did not even > >>> imagine implementing SIGFPE, SIGILL, SIGTRAP, which I thought could not > >>> be time critical anyway, for the reasons explained earlier. So, my > >>> question (rather to Henri) is: what would we need SIGFPE, SIGILL, > >>> SIGTRAP in an real-time application for? > >> I agree it might be unusual. For the tracing use case: the SIGTRAP we > >> use as a means for tracing whether code is actually executed, just > >> like breakpoints, we exchange the code to 0xcc and handle the > >> exceptions do book-keeping but don't stop the task. We know this has > >> overhead, it also had when using our old OS. The old OS handled it in > >> an accepted amount of time. Using the Xenomai kernel it also works, > >> however the overhead is not acceptable anymore. > >> Installing a floating point exception handler was also provided to our > >> customers with the old OS and we have to make that available now too. > >> So actually it is all because of legacy reasons, we have to provide > >> similar functionality as with the old OS. > >> > >> I'm afraid we cannot mimic enough so it suits our use cases. We need > >> the fault context to handle the exception and to set the IP one > >> instruction back. > > > > So you need the signal rebase over the mayday support I merged a few > > months ago. Back to square one I'm afraid, this won't be available soon, > > albeit this might happen in the 2.6 timeframe. We'll see. > > Well, not necessarily, the fault handler may set the IP, suspend the > task, wake-up the dedicated fault-handler thread, then, the dedicated > fault-handler may wake-up the suspended task when the work has been done. >
This is not exactly what I'd call a straightforward solution (which was the point of offloading the work to userland) . If one knows how to do that within the Xenomai core, he could just re-route the mayday mechanism, no need for sideways. -- Philippe. _______________________________________________ Xenomai-help mailing list [email protected] https://mail.gna.org/listinfo/xenomai-help
