System management interrupt

[Emmanuel Pacaud]

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 ?

	Regards,

		Emmanuel.