Manual browser: cpu_need_resched(9)

CPU_NEED_RESCHED(9) Kernel Developer's Manual CPU_NEED_RESCHED(9)


cpu_need_reschedcontext switch notification


#include <sys/cpu.h>

cpu_need_resched(struct cpu_info *ci, int flags);


The cpu_need_resched() function is the machine-independent interface for the scheduler to notify machine-dependent code that a context switch from the current LWP, on the cpu ci, is required. This event may occur if a higher priority LWP appears on the run queue or if the current LWP has exceeded its time slice.

If RESCHED_KPREEMPT flag is specified in flags and __HAVE_PREEMPTION C pre-processor macro is defined in <machine/intr.h>, machine-dependent code should make a context switch happen as soon as possible even if the cpu is running the kernel code.

If RESCHED_IMMED flag is specified in flags, machine-dependent code should make a context switch happen as soon as possible. In that case, for example, if ci is not the current processor, cpu_need_resched() typically issues an inter processor call to the processor to make it notice the need of a context switch as soon as possible.

Typically, the cpu_need_resched() function will perform the following operations:

  • Set a per-processor flag which is checked by userret(9) when returning to user-mode execution.
  • Post an asynchronous software trap (AST).
  • Send an inter processor interrupt to wake up cpu_idle(9).
July 31, 2010 NetBSD 7.0