cpu_need_resched(9) - NetBSD Manual Pages

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CPU_NEED_RESCHED(9)    NetBSD 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, struct lwp *l, 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 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().


SEE ALSO

     sched_4bsd(9), userret(9)

NetBSD 10.1                    November 17, 2019                   NetBSD 10.1