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.Dd November 17, 2019 .Dt CPU_NEED_RESCHED 9 .Os .Sh NAME .Nm cpu_need_resched .Nd context switch notification .Sh SYNOPSIS n sys/cpu.h .Ft void .Fn cpu_need_resched "struct cpu_info *ci" "struct lwp *l" "int flags" .Sh DESCRIPTION The .Fn 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 .Fa l , on the cpu .Fa 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. .Fa l is the last LWP observed running on the CPU. It may no longer be running, as .Fn cpu_need_resched can be called without holding scheduler locks.
p If the .Dv RESCHED_KPREEMPT flag is specified in .Fa flags and .Dv __HAVE_PREEMPTION C pre-processor macro is defined in n 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 .Dv RESCHED_KPREEMPT flag is not specified, then .Dv RESCHED_UPREEMPT is specified instead.
p If the .Dv RESCHED_IDLE flag is specified in .Fa flags , the last thread observed running on the CPU was the idle LWP.
p If .Dv RESCHED_REMOTE flag is specified in .Fa flags , the request is not for the current CPU. The opposite also holds true. If .Fa ci is not the current processor, .Fn 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.
p .Fn cpu_need_resched is always called with kernel preemption disabled.
p Typically, the .Fn cpu_need_resched function will perform the following operations: l -bullet -offset indent t Set a per-processor flag which is checked by .Xr userret 9 when returning to user-mode execution. t Post an asynchronous software trap
q Tn AST . t Send an inter processor interrupt to wake up .Xr cpu_idle 9 and/or force an user process across the user/kernel boundary, thus making a trip through .Fn userret . .El .Sh SEE ALSO .Xr sched_4bsd 9 , .Xr userret 9