// We will only check <candidates> with extenders that support preemption.
// Extenders which do not support preemption may later prevent preemptor from being scheduled on the nominated
// node. In that case, scheduler will find a different host for the preemptor in subsequent scheduling cycles.

// stack bound to a value that will cause the next stack bound check
// to fail and enter the stack growth implementation, which will
// detect that it was actually a preemption and redirect to preemption
// handling.
//
// Preemption at asynchronous safe-points is implemented by suspending
// the thread using an OS mechanism (e.g., signals) and inspecting its
// state to determine if the goroutine was at an asynchronous

	// NodeInfoSnapshot because we don't guarantee that they will be the same.
	// For example, during preemption, we may pass a copy of the original
	// nodeInfo object that has some pods removed from it to evaluate the
	// possibility of preempting them to schedule the target pod.
	Filter(ctx context.Context, state *CycleState, pod *v1.Pod, nodeInfo *NodeInfo) *Status
}

	// saved by entersyscall here.
	entersyscall()

	// Tell asynchronous preemption that we're entering external
	// code. We do this after entersyscall because this may block
	// and cause an async preemption to fail, but at this point a
	// sync preemption will succeed (though this is not a matter
	// of correctness).
	osPreemptExtEnter(mp)

	mp.incgo = true

	vdsoPC uintptr // PC for traceback while in VDSO call

	// preemptGen counts the number of completed preemption
	// signals. This is used to detect when a preemption is
	// requested, but fails.
	preemptGen atomic.Uint32

	// Whether this is a pending preemption signal on this M.
	signalPending atomic.Uint32

	// pcvalue lookup cache
	pcvalueCache pcvalueCache

		// will fit due to the preemption. It is also possible that a different pod will schedule
		// into the resources that were preempted, but this is harmless.

		if !fwk.HasPostFilterPlugins() {
			logger.V(3).Info("No PostFilter plugins are registered, so no preemption will be performed")

	// We are interested in preempting user Go code, not runtime code.
	// If we're holding locks, mallocing, or preemption is disabled, don't
	// preempt.
	// This check is very early in newstack so that even the status change
	// from Grunning to Gwaiting and back doesn't happen in this case.
	// That status change by itself can be viewed as a small preemption,

	dontfreezetheworld: by default, the start of a fatal panic or throw
	"freezes the world", preempting all threads to stop all running
	goroutines, which makes it possible to traceback all goroutines, and
	keeps their state close to the point of panic. Setting
	dontfreezetheworld=1 disables this preemption, allowing goroutines to
	continue executing during panic processing. Note that goroutines that

	// Any time we acquire a traceLocker, we may flush a trace buffer. But
	// buffer flushes are rare. Record the lock edge even if it doesn't happen
	// this time.
	lockRankMayTraceFlush()

	// Prevent preemption.
	mp := acquirem()

	// Acquire the trace seqlock. This prevents traceAdvance from moving forward
	// until all Ms are observed to be outside of their seqlock critical section.
	//

	// cost of maintaining this consistency is low. We're not going to hold this semaphore
	// for very long and most STW periods are very short.
	// Once we hold worldsema, prevent preemption as well so we're not interrupted partway
	// through this. We want to get this done as soon as possible.
	semacquire(&worldsema)
	mp := acquirem()

	// Advance the generation or stop the trace.