System management interrupt

[Emmanuel Pacaud]

Le vendredi 17 novembre 2006 à 13:44 +0100, Emmanuel Pacaud a écrit :
> Le mardi 14 novembre 2006 à 13:56 +0100, Emmanuel Pacaud a écrit :
> > Hi,
> > 
> > I'm working on a realtime setup based on rtai/linux running on a dell
> > precision workstation 690 dual xeon.
> > 
> > When measuring execution time of a real time interrupt handler (which
> > means all interrupts are disabled), it looks like sometimes execution of
> > interrupt handler code is interrupted for 10 µs.
> > 
> > That measurement is done with a code that looks like:
> > 
> > 	t_start = rdtsc ();
> > 	udelay(5);
> > 	t_stop = rdtsc ();
> > 
> > where (t_stop - t_start) distribution has a peak centered at 5 µs, and a
> > smaller peak at 15 µs.
> > 
> > Since all interrupts are disabled, our assumption is this issue come
> > from a SMI. 
> > 
> > That's something discussed in rtai documentation, which explains we have
> > to disable SMI in order to obtain good real time performances.
> > 
> > I've tried to unset the GBL_SMI_EN bit in LPC Interface Bridge SMI_EN 
> > Register, but without success (the second peak is still there).
> > 
> > Here are my questions:
> > 
> > Is the assumption of a SMI interrupt blocking the execution of a real
> > time interrupt handler code reasonnable ?
> > 
> > If so, does someone knows if it's possible to disable SMI interrupts on
> > a dell precision 690, and if so, how ?
> > 
> > If not, what could be the cause of what the lengthened execution time ?
> 
> Hi,
> 
> It looks like nobody here is able to answer these questions. My be it's
> not the right place for such discussion. Is there another mailing list
> where I could find dell hardware experts ?

Really, no hope ?

	Emmanuel.