Peter Soetens wrote: > On Wed, Sep 30, 2009 at 16:27, Gilles Chanteperdrix > <gilles.chanteperd...@xenomai.org> wrote: >> Peter Soetens wrote: >>> On Tue, Sep 29, 2009 at 19:31, Gilles Chanteperdrix >>> <gilles.chanteperd...@xenomai.org> wrote: >>>> Hi guys, >>>> >>>> full of energy after this tremendous first XUM, I would like to start a >>>> discussion about what people would like to see in the 2.5 branch. >>> So if we answer positively, we'll delay the release ? I'd rather get >>> 2.5 out, and develop any new stuff on 2.6. I would also expect that >>> this list (or part of ) goes to xenomai-help too. >> The facts are: >> - our release cycle is long; >> - we want to keep the ABI stable for each branch. >> So, anything that we want "soon" and that breaks the ABI should be done >> in the 2.5 branch, otherwise will have to wait 2.6. > > Ok, but there is stuff in 2.5 I want "soon" too, which you would be delaying. > >>>> Here is a first list, please feel free to criticize it: >>>> - signals in primary domain (something that we almost forgot) >>> I refrain from using signals in my apps. They only cause disaster when >>> using 3rd party libraries. Only Ctrl-C (quit) and debugger signals are >>> used, and a switch from primary to secondary is perfectly acceptable >>> in these two cases. >> Yes, signals is a bit of a misnomer, what we actually want is for the >> kernel to be able to cause the execution of an asynchronous callback in >> user-space. For the native skin, it would be for the implementation of >> some hooks. For the posix skin, it would be for the implementation of >> signasl. The implementation of posix timers is based on signals (except >> for SIGEV_THREAD, but who uses SIGEV_THREAD in an rt app...), having >> them cause a switch to secondary mode make them unusable for practical >> purposes. So, with the current version of Xenomai posix skin, you have >> to implement your own timer method, having for instance a thread which >> nanosleep()s until the next timer expiry and then executes the callback. > > Ok, but I don't use posix timers for the reasons above. I use > clock_nanosleep instead, which offers the same functionality.
Any sane skin should offer timer services... Using nanosleep is a workaround for the lack of this feature. > >>>> - xnsynch_acquire using atomic_cmpxchg unconditionally (no #ifdefs) >>> This is too core for me. >>> >>>> - statistics of all mapped named heaps in /proc/xenomai/heap >>> Don't use heaps since we do all in user space (and I had the >>> impression that heap was for kernel<->user.) >>> >>>> - unwapped access to user-space posix skin methods >>> I wouldn't know why I need this. Do you we link with libpthread >>> instead of libpthread-rt ? >> Well the wrap thing is a bit cumbersome. And having the calls be named >> with exactly the posix name is useful only if you intend to compile >> exactly the same code for xenomai and other posix systems. Otherwise, >> you could decide to use a little prefix or suffix to each posix skin >> service, and avoid the wrapping clumsyness. > > So like we did in the RTAI days. Maybe we can use rt_ by (safe!) > default and allow a #define in case the users wants to use the > wrapping and is aware that he needs to use the wrapping during > linking. No, no macros, just aliases at binary level. Probably a separate header too. > >>>> - fast semaphores in user-space >>> I donn't know why I wouldn't need this. >>> >>>> - syscall-less select ? >>> Since a syscall is not per-se bad (?) I also don't see what to win here. >> syscall are expensive (which is why we do syscall-less mutexes for >> instance). The idea would be to put the bitfield with the ready file >> descriptors in a shared heap, to avoid going for the syscall if fds are >> already ready when entering select(). The scenario where we would gain >> is on a loaded system, which is exactly when we want to avoid useless >> syscalls. > > Then I'm tempted to be in favour, although I'd like to confirm first > that select() is not broken as it is now. Are syscalls expensive > because I'm running Xenomai, or is this the case in vanilla Linux too > ? Do we try to be better than Linux (until they use a similar 'fix' in > libc) ? No, syscalls are expensive because they are two context switches from user-space to kernel-space and back. As for the implementation of select, Xenomai's implementation is a different trade-off than Linux'es. Typically, you get O(1) performance, whereas with Linux, you get O(n) peformance. n being the number of descriptors in the fdset. People will tell you that it does not matter since user-space scanning the fdset returned by select is O(n), but it is a much smaller big O (testing a bit). > >>>> Actually, there are already a lot of things. >>>> So, what do you think? >>> I'm uttermost concerned with stability and to a lesser extent >>> performance. I regard every feature change as changing those two >>> criteria for the worse (unless its a feature that fixes a bug). >> Well... I disagree. Even when fixing bugs we can introduce other bugs. >> What matters if you aim for stability and performance is improving the >> tests, not avoiding modifications. > > You got me. But until the tests are improved, I beg you to be careful ;-) There is something I realized when watching Niklaus Giger's presentation, it is that users should distrust the maintainers' testing and should run their own tests, I think it is a sane behaviour. I do not mean that we should not improve our testing, but simply that our tests can not cover the way all users use Xenomai. -- Gilles. _______________________________________________ Xenomai-core mailing list Xenomaifirstname.lastname@example.org https://mail.gna.org/listinfo/xenomai-core