On 08/02/2013 04:53 PM, Marco Stornelli wrote:
- how to assign an interrupt (e.g. a dedicated timer) to the
subsystem ?
Interrupt handler are kernel thread, so you can schedule your kernel
thread on your "normal" cpu.
Sorry. I don't understand.
The point I'd like to make is, that for really low latency stuff the ISR
needs to take place immediately when the hardware fires an interrupt.
As the Linux kernel will (for the SMP CPUs it handles) need to disable
interrupt in certain cases, it is essential that the "really low
latency" interrupt is assigned to the AMP cpu (that the Kernel will
never touch).
AFAIC, no latency for cpu "under affinity".
That would be great but it need the stuff described above.
In fact the interrupt would need to be assigned to the AMP cpu by some
hardware means (that I don't know anything about yet), and not be
"forwarded" in any way from some other cpu (which is managed by the
Kernel) and thus might be in a "interrupt disable state at some point in
time.
(and how
many cpu cycles at max are needed to enter the ISR) ?
It's difficult to answer to this question because the performance
depends on your system. From my last statistics I saw that with an rt
linux kernel you can stay below 50us for the interrupt latency.
Of course (sorry for unclear language). I tried to ask for a pointer to
start developing an algorithm that allows to predict the max latency the
system can offer.
Here we could try to do these calculations as well with a "really
dedicated AMP" CPU and with a system using "preempt-rt" and "cpu
affinity" appropriately. to see if a more "standard" way to do things
might be good enough.
Thanks for your answers,
-Michael
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