Philippe Gerum wrote: > Gilles Chanteperdrix wrote: >> Jan Kiszka wrote: >> > (...)As Xenomai does not support hard-RT signal delivery yet (...) >> >> This is the next feature missing to the POSIX skin. I would like to >> implement this, but I am not sure which way to go : >> - either, if it is possible, getting Linux signals services to run in >> every domain at Adeos level, by replacing spinlocks with spinlocks_hw >> and such kind of tricks; > > Would be a nightmare, I think. Way too many paths are involved in the > vanilla kernel, and this would be overkill wrt what we want to do. > Actually, what we need is basically exposing the nucleus signal > interface to user-space, and map Linux RT signals over nucleus signals. > Other (non-RT) Linux signals would keep on being handled in secondary > mode the way they are now. > >> - or adding a generic service at the adeos layer (a hook called when >> returning to user-space), building a generic user-space signals >> service at the nucleus level, and finally building all posix signals >> services on top of this. > > A (maybe easier) third option would be to generalize some kind of > pseudo-asynchronous call support, with a worker thread operating on a > dedicated priority level inside applications registering for > asynchronous notifications. The kernel-side would handle the server > wakeups, providing a unified interface for pending on hooks, signals, > watchdogs etc. It would also need to properly multiplex those events > notified from within the skins, and wake up the right pending server in > user-space, which would in turn fire the user provided handler, all in > primary mode. In any case, this would not be more costly latency-wise > than implementing mere callouts, since most of the switching cost comes > from the MMU switch, which we would have to do in both cases, anyway.
We would need a "shadow" priority level for each real one so that those handlers do not cause any priority inversions (the main RT issue of servers). Moreover, it would require a bulk of extra threads, actually one per used prio level, to handle all those calls with the correct priority. My feeling: too costly, memory-wise. Jan
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