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i remember using DEC VAX ancillary control processes and writing knob and trackball device drivers in user land in the early 80s. I tried to find something describing this but I think it is lost to antiquity.
does anyone know how they did it? i don't remember ever losing an interrupt or affecting the rest of the system but then again everything is relative.
When we applied user-level interrupts in N extension to the Unix-like OS, there is no way to directly handle user-level interrupts in userspace bypassing the kernel. This makes little use of the user-level interrupt mechanism.
In this proposal, we provide a hardware-assisted context switch mechanism to accelerate handling interrupts in the U-mode of Unix-like OS. Our proposal is implemented on the QEMU simulator and KVM virtualization architecture. Evaluation results show that our
proposal improves the block performance by 2.63% to 7.56%. Also, more benefits can be gained by combining this proposal with some other optimizations.
The attachment is the detailed proposal. Any comments are welcome.
Mark I Himelstein
CTO RISC-V International