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 can imagine some benefit to a hypothetical improved SENDUIPI with idential user semantics but that supported a proper interaction with the scheduler and blocking syscalls.  But that's not what's documented in the ISE...)

--Andy