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

# NAME

`cpu_need_resched` —
context switch notification

# SYNOPSIS

`#include <sys/cpu.h>`

void
`cpu_need_resched`(struct cpu_info *ci, int flags);

# DESCRIPTION

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).

# SEE ALSO

sched_4bsd(9), userret(9)

July 31, 2010 | NetBSD 9.5