On Wed, 21 Jun 2006, Ryan McAvoy wrote:
> > First, whenever sending mail about the -rt patch, always CC Ingo (and
> > perhaps Thomas Gliexner and myself).
>
> Thanks, I will do that.
Ingo is the important one. Thomas and I are just the janitors
Although Thomas is chief janitor :)
>
> > 2.6.15 had lots of problems with -rt. Mainly the patch went through some
> > major rework, and Ingo was busy getting mutexes into mainline. So the
> > 2.6.15-rtX was sort of neglected. It would be best to use 2.6.16-rtX and
> > maybe even 2.6.17-rtX
> >
> > Which also comes the question: Which -rt patch are you actually trying?
>
> patch-2.6.15-rt21 . I have also tried using the 2.6.16 kernel and
Hmm, 15-rt21 may have stabilized a bit. But I do still think the 16 series
is much more stable.
> patch-2.6.16-rt29 and have the same problems with it. (I may be
> constrained in having to use a 2.6.15 kernel ... but would be happy to
> get 2.6.16 working /stable as a starting point.)
>
> > Yep, try the following patch: (completey untested since I don't have a
> > mips machine).
> >
> > config RWSEM_GENERIC_SPINLOCK
> > bool
> > - depends on !PREEMPT_RT
> > + depends on PREEMPT_RT
> > default y
>
> I did just that when I first started with these patches and did
> succeed in getting it compiling and booting. The resulting kernel,
> however, is very unstable and hangs frequently with no output. (It
> will hang within hours if left idle. I can hang it more quickly by
> attempting to use it). I have deadlock detection turned on and have
> confirmed that it does produce output at least for some deadlocks:
> http://groups.google.com/group/linux.kernel/browse_frm/thread/1559667001b7da2d/2558b539a5adc660?lnk=st&q=realtime+preempt+mips&rnum=2&hl=en#2558b539a5adc660
> In the more common hangs though, I get no output.
That output looks like it had a deadlock on the serial output of sysrq
key. But that back trace looks screwy.
>
> I decided to review the changes I made in getting it to compile and
> was hoping that this one may be the cause of the instability. I
> thought that perhaps this change was incorrect because
> include/asm-mips/rwsem.h is introduced by the rt-preempt patch and
Ha, you're right! (added John Cooper to this so he can clean up this mess
;)
> would only be used if RWSEM_GENERIC_SPINLOCK was off. [As well, it
> seemed like something fundamental enough to account for the general
> instability I am seeing.]
>
Perhaps you can post all the changes you made as a patch to see if
something else is wrong. It might also be best to see if you can get the
latest working (2.6.17-rtX) and work your way backwards to the kernel
version you really need.
-- Steve
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