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cpu_need_resched(9) [netbsd man page]

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

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

Check Out this Related Man Page

USERRET(9)						   BSD Kernel Developer's Manual						USERRET(9)

userret -- return path to user-mode execution SYNOPSIS
#include <sys/lwp.h> #include <sys/sched.h> void userret(struct lwp *l); DESCRIPTION
The userret() function is executed after processing a trap (e.g., a system call or interrupt) before returning to user-mode execution. The implementation is machine dependent and is never invoked from machine-independent code. The function prototype for each architecture may be different to the prototype above, however the functionally provided by the userret() function on each architecture is essentially the same. Specifically, the userret() function performs the following procedure: o Detect a change in the signal disposition of the current process and invoke postsig(9) to post the signal to the process. This may occur when the outcome of the trap or syscall posted a signal to the process (e.g., invalid instruction trap). o Check the want_resched flag to see if the scheduler requires the current process to be preempted by invoking preempt(9) (see cpu_need_resched(9)). This may occur if the clock interrupt causes the scheduler to determine that the current process has com- pleted its time slice. o Update the scheduler state. SEE ALSO
cpu_need_resched(9), postsig(9), preempt(9), scheduler(9) BSD
December 20, 2005 BSD
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