What is Rescheduling interrupts (RES)? What causes it? How is it handled in Linux kernel?
What is the difference between "RES: Rescheduling interrupts" and "LOC: Local timer interrupts"? What is responsible to fire the RES interrupt? Is LOC same as the general timer interrupt that is generated by the Timer h/w in the processor?
Also, please give some clarity on what part of the scheduler is invoked during the timer interrupt and the RES interrupt? How it happens in Linux kernel?
Thanks in advance.
Answer
Rescheduling interrupts are the Linux kernel's way to notify another CPU-core to schedule a thread.
On SMP systems, this is done by the scheduler to spread the load across multiple CPU-cores.
The scheduler tries to spread processor activity across as many cores as possible. The general rule of thumb is that it is preferable to have as many processes running on all the cores in lower power (lower clock frequencies) rather than have one core really busy running at full speed while other cores are sleeping.
Rescheduling interrupts are implemented using Inter-Processor Interrupts (IPI). For more details checkout this article on Rescheduling Interrupts on Linux.
Local timer interrupts are raised by the APIC for a specific CPU-core. Only that CPU-core receives the interrupts and handles them. For a brief description of its various advantages, checkout this answer.