Timer interrupts is supposed to cause scheduling and scheduler may or
may not pick up your last process(we always use the term "task" in
kernel space) after handling timer interrupt.

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Sorry if I may disagree, correct me if wrong. Timer interrupt and scheduler is two different thing. I just counted in the "drivers" subdirectory, there are at least more than 200 places where "setup_timer()" is called, and these have nothing to do with scheduling. For eg, heartbeat operation etc. Not sure I misunderstood something?