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I recently started diving into low level OS programming. I am (very slowly) currently working through two older books, XINU and Build Your Own 32 Bit OS, as well as some resources suggested by the fine SO folks in my previous question, How to get started in operating system development.
It could just be that I haven't encountered it in any of those resources yet, but its probably because most of these resources were written before ubiquitous multicore systems, but what I'm wondering is how interrupts work in a multicore/multiprocessor system.
For instance, say the DMA wants to signal that a file read operation is complete. Which processor/core acknowledges that an interrupt was signaled? Is it the processor/core that initiated the file read? Is it whichever processor/core that gets to it first?
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A multicore processor is an integrated circuit that has two or more processor cores attached for enhanced performance and reduced power consumption. These processors also enable more efficient simultaneous processing of multiple tasks, such as with parallel processing and multithreading.
Most modern general purpose microprocessors handle the interrupts the same way. When a hardware interrupt occurs the CPU stops executing the instructions that it was executing and jumps to a location in memory which either contains the interrupt handling code or an instruction branching to the interrupt handling code.
When an interrupt occurs, the hardware saves pertinent information about the program that was interrupted and, if possible, disables the processor for further interrupts of the same type. The hardware then routes control to the appropriate interrupt handler routine.
When a hardware component (such as a disk controller or an Ethernet NIC) needs to interrupt the work of the CPU, it triggers an interrupt. The interrupt notifies the CPU that an event occurred and the CPU should suspend its current work to deal with the event.
Looking into the IoConnectInterrupt function you can find the ProcessorEnableMask that will select the cpu's that allowed to run the InterruptService routine (ISR).
Based on this information i can assume that somewhere in the low level (see Adam's post) it's possible to specify where to route the interrupt.
On the side note file operation is not really related to the interrupts and/or dma directly. File operation is file system concept that translated to something low level depend on which bus you filesystem located it might be IDE or SATA disk or it might be even usb storage in this case sector read will be translated to 3 logical operation over usb bus, there will be interrupt served by usb host controller driver, but it's not really related to original file read operation, that was probably split to smaller transaction any way.
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In the old days the interrupt went to all processors. In modern times some kinds of hardware can be programmed by an OS to send an interrupt to one particular processor. Of course if you could choose a processor dynamically instead of statically, you wouldn't want to send the interrupt to whichever processor initiated the I/O, you'd want to send it to whichever processor is least burdened at the present time and can most efficiently start the next I/O operation, and/or whichever processor is least burdened at the present time and can most efficiently execute the thread that was waiting for the results.
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