Message Signaled Interrupts - Advantages Over Pin-based Interrupts

Advantages Over Pin-based Interrupts

While more complex to implement in a device, MSI has some significant advantages.

On the mechanical side, fewer pins makes for a simpler, cheaper, and more reliable connector. While this is no advantage to the standard PCI connector, PCI Express takes advantage of these savings.

MSI increases the number of interrupts that are possible. While conventional PCI was limited to 4 interrupts per card (and, because they were shared among all cards, most used just 1), message signaled interrupts allow dozens of interrupts per card, when that is useful.

There is also a slight performance advantage. In software, a pin-based interrupt could race with a posted write to memory. That is, the PCI device would write data to memory and then send an interrupt to indicate the DMA write was complete. However, a PCI bridge or memory controller might buffer the write in order to not interfere with some other memory use. The interrupt could arrive before the DMA write was complete, and the processor could read stale data from memory. To prevent this race, interrupt handlers were required to read from the device to ensure that the DMA write had finished. This read had a moderate performance penalty. An MSI write cannot pass a DMA write, so the race is eliminated.

Read more about this topic:  Message Signaled Interrupts

Famous quotes containing the words interrupts and/or advantages:

    An entertainment is something which distracts us or diverts us from the routine of daily life. It makes us for the time being forget our cares and worries; it interrupts our conscious thoughts and habits, rests our nerves and minds, though it may incidentally exhaust our bodies. Art, on the other hand, though it may divert us from the normal routine of our existence, causes us in some way or other to become conscious of that existence.
    Sir Herbert Read (1893–1968)

    A woman might claim to retain some of the child’s faculties, although very limited and defused, simply because she has not been encouraged to learn methods of thought and develop a disciplined mind. As long as education remains largely induction ignorance will retain these advantages over learning and it is time that women impudently put them to work.
    Germaine Greer (b. 1939)