P4 dual xeon problems

Gunter Cieters gcieters at broadcom.com
Thu Sep 27 07:58:09 UTC 2001

My apologies for posting my first mail with an incorrect

> > We are running the RTEMS native host environment (Linux
> > target) on a standard Linux Redhat 7.1 distribution. Lateley,
> > we are bugged by some RTEMS crashes on a dual P4
> > xeon system. The crashes disappear when we boot Linux
> > in uniprocessor mode.
> > 
> > Is there anybody who would know a reason why the RTEMS
> > host environment would not run on the P4 SMP system ? (we
> > would like to rule out RTEMS and proceed in upgrading the Linux
> > kernel but it is a little bit weird that the crashes only
> > appear when we are doing RTEMS runs).
> This is an interesting one that I have never heard of before.  The
> RTEMS unix port (aka synthetic target) runs completely in user space as
> a normal Linux process.  It only uses a handful of Linux system operations
> like sigalarm and signal processing for a clock tick and setjmp/longjmp for
> context switches.  I don't know anything it can do that should trip up the
> kernel directly UNLESS ...
> <hypothesis mode on>
> RTEMS could be using some service heavily that is not truly MP safe.
> For example, we repeatedly fire the clock tick.  Say that there is a bug
> in the signal processing code that our heavy use of SIGALRM is tripping.
> My gut feeling is that RTEMS is somehow tripping a bug where something
> is not properly protected in Linux.
> <hypothesis mode off> 
> Does the kernel crash or just the RTEMS application?

The RTEMS application halts with segfault or sigill (the place
where this happens is a bit random although there may be a relationship with
floating point usage when looking to the stack traces).
If RTEMS is MP safe then it is possible that the Linux kernel has a
problem with correct save/restore of the floating point registers. We have
ran in this before when using the MMX extensions on Linux (we got around
that particular problem by applying a kernel patch).

I'll keep this mailing list informed if we find anything related to kernel

thanks for your answer,
Cieters Gunter

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