cpu_need_resched(9) - NetBSD Manual Pages

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

cpu_need_resched -- context switch notification
#include <sys/cpu.h> void cpu_need_resched(struct cpu_info *ci, struct lwp *l, 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 l, 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. l is the last LWP observed running on the CPU. It may no longer be running, as cpu_need_resched() can be called without holding scheduler locks. If the 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 in kernel mode. If the RESCHED_KPREEMPT flag is not spec- ified, then RESCHED_UPREEMPT is specified instead. If the RESCHED_IDLE flag is specified in flags, the last thread observed running on the CPU was the idle LWP. If RESCHED_REMOTE flag is specified in flags, the request is not for the current CPU. The opposite also holds true. 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. cpu_need_resched() is always called with kernel preemption disabled. 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) and/or force an user process across the user/kernel boundary, thus making a trip through userret().
sched_4bsd(9), userret(9) NetBSD 10.99 November 17, 2019 NetBSD 10.99
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