On Tue, Sep 28, 2021 at 09:31:34PM -0700, Andy Lutomirski wrote:
On Mon, Sep 13, 2021, at 1:01 PM, Sohil Mehta wrote:
User Interrupts Introduction
User Interrupts (Uintr) is a hardware technology that enables delivering interrupts directly to user space.
Today, virtually all communication across privilege boundaries happens by going through the kernel. These include signals, pipes, remote procedure calls and hardware interrupt based notifications. User interrupts provide the foundation for more efficient (low latency and low CPU utilization) versions of these common operations by avoiding transitions through the kernel.
...
I spent some time reviewing the docs (ISE) and contemplating how this all fits together, and I have a high level question:
Can someone give an example of a realistic workload that would benefit from SENDUIPI and precisely how it would use SENDUIPI? Or an example of a realistic workload that would benefit from hypothetical device-initiated user interrupts and how it would use them? I'm having trouble imagining something that wouldn't work as well or better by simply polling, at least on DMA-coherent architectures like x86.
I was wondering the same thing. One thing came to mind:
An application that wants to be *interrupted* from what it's doing rather than waiting until the next polling point. For example, applications that are CPU-intensive and have green threads. I can't name a real application like this though :P.
Stefan