Messages in this thread |  | | Date | Tue, 27 Aug 2002 13:41:54 -0400 | From | Mark Hounschell <> | Subject | Re: interrupt latency |
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"Wessler, Siegfried" wrote: > > Hello, > > I am running and will in near future kernel 2.4.18 on an embedded system. > > I have to speed up interrupt latency and need to understand how in what > timing tasklets are called and arbitraded. > > I have to dig deep, but the kernel tree is quiet huge. As a non kernel > programmer I ask you, if anyone could give me a hint, where to start reading > from and which kernel source to pick first. > > Any help highly appreaciated. > (BTW: I will not bother you personaly with further questions unless you give > permission.) > > What's behind it: We patched NMI and do some stuff we have to do very > regularly in there. After NMI we have to quiet fast start a kernel or even a > user space function with low latency. Also I measured 8 milliseconds after a > hardware interrupt before the corresponding interrupt function is called. At > RTI time it is even longer (around 12 microseconds). Need to find a way to > exactly understand why, and maybe speed up a bit. > > Thank You. > Siegfried.
I've found that with the combination of process affinity and irq affinity you can get very good interrupt latency/determinism. We use a pci card that has some external interrupts and some 250ns resolution timers and have found the interrupt latency/determinism of the external interrupts to be more than exceptable as long as the process and irq of that pci card are forced to one cpu and ALL other processes/irq's are forced to another cpu. Of coarse you need an SMP box for best results. We found that with a UMP box you can get the latency but there is no determinism to that latency.
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