Minimizing Overhead Work

Minimizing Overhead Work

A certain amount of CPU time must be spent on general housekeeping. Since this work is done by the kernel and triggered by interrupts, it can interfere with the operation of a real-time process. However, you can remove almost all such work from designated CPUs, leaving them free for real-time work.

First decide how many CPUs are required to run your real-time application (regardless of whether it will be scheduled normally, or as a gang, or by the Frame Scheduler). Then apply the following steps to isolate and restrict those CPUs. The steps are independent of each other. Each needs to be done to completely free a CPU.

Assigning the Clock Processor
Assigning the fasthz Processor
Unavoidable Timer Interrupts
Isolating a CPU From Sprayed Interrupts
Assigning Interrupts to CPUs
Understanding the Vertical Sync Interrupt
Restricting a CPU From Scheduled Work
Isolating a CPU From TLB Interrupts
Making a CPU Nonpreemptive