Philippe Gerum wrote: > On Tue, 2007-06-12 at 19:59 +0200, Jan Kiszka wrote: >> Gilles Chanteperdrix wrote: >>> Jan Kiszka wrote: >>>> Philippe Gerum wrote: >>>> >>>>> On Tue, 2007-06-12 at 08:42 +0200, M. Koehrer wrote: >>>>> >>>>>> Hi everybody, >>>>>> >>>>>> I want to know why the --enable-smp option for "configure" of Xenomai is >>>>>> used when there >>>>>> is already the corresponding option selected with the kernel >>>>>> configuration? >>>>> --enable-smp is only used when you want the user-space side to _require_ >>>>> SMP support to be present into the running kernel; i.e. for some (weird) >>>>> reason, your application really needs this. Xenomai libraries don't care >>>>> whether SMP support is enabled or not, they are not sensitive to that >>>>> issue (see the "weak" status of this option in README.INSTALL) >>>> Switchtest bases some compile-time decisions on CONFIG_SMP. Nitpicking, >>>> OK, but I wonder if this is required. Gilles? >>> If you do not enable the smp option, switchtest will only use one cpu. >>> The reason why I made this is that, on some UP machine, (probably arm, >>> but I do no longer remember) sysconf(_SC_NPROCESSORS_ONLN) did not work. >> Welcome to embedded hell :-/. What was the effect precisely? Can we >> detect this during runtime? The point is I see people trying this test >> on SMP without providing the right switch to configure. Would be a pity >> IMHO. >> >> At this chance: I also noticed problems with our sched_setscheduler >> detection and bfin's uClibc. Compilations works, linking fails - they >> provide headers, but lack implementations. Patch suggestion will follow. >> >> And my pthread_spin_lock detection got nicely vaporised on bfin once >> again. I'm considering to switch back to the original configure-based >> detection. > > Notice that you have no atomic ops available on Blackfin CPUs, and to > emulate them, you would have to mask interrupts, which you can't do in > user-space (privileged instruction). So you will always end up issuing a > syscall under the hood (bfin_spinlock), that does some kind of spinlock > emulation from kernel space. Next kernel releases might improve things > by allowing to jump to atomic emulation routines directly from > user-space, but this is not yet available AFAIK. IOW, don't expect > performance improvements from user-space locking, yet.
For now my point was the old uClibc issue "define _POSIX_SPIN_LOCKS, but avoid to implement it". Blackfin's toolchain managed to do the second part differently, and no longer detectable without configure's help. > >> Enough of the moaning. >> > > Still, this is quite a fun architecture to work with. Yeah, it basically worked here already (with latest release, to answer your other mail), some Xenomai tests (non-POSIX) used to run. But now I'm a bit off-road (SVN head) to apply patches and fix quirks I came across. That's where the fun really starts... :) Jan
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