CPU_NEED_RESCHED(9) BSD 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:
o Set a per-processor flag which is checked by userret(9) when returning to user-mode execution.
o Post an asynchronous software trap (AST).
o Send an inter processor interrupt to wake up cpu_idle(9).
SEE ALSO
sched_4bsd(9), userret(9)
BSD
July 31, 2010 BSD
