// 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

// of candidates that should be shortlisted for dry running preemption.
func (pl *DefaultPreemption) GetOffsetAndNumCandidates(numNodes int32) (int32, int32) {
	return rand.Int31n(numNodes), pl.calculateNumCandidates(numNodes)
}

// This function is not applicable for out-of-tree preemption plugins that exercise
// different preemption candidates on the same nominated node.

	// this fails, a preemption is in progress, so the thread must
	// wait for the preemption. preemptM also CASes this from 0 to
	// 1. If this fails, the preemption fails (as it would if the
	// PC weren't in Go code). The value is reset to 0 when
	// returning from external code or after a preemption is
	// complete.
	//
	// TODO(austin): We may not need this if preemption were more

	for nodeName, victims := range nodeNameToVictimsCopy {
		// Try to do preemption on extender side.
		nodeInfo, _ := nodeInfos.Get(nodeName)
		extenderVictimPods, extenderPDBViolations, fits, err := f.selectVictimsOnNodeByExtender(logger, pod, nodeInfo)
		if err != nil {
			return nil, err
		}
		// If it's unfit after extender's preemption, this node is unresolvable by preemption overall,
		// let's remove it from potential preemption nodes.

			ctxt.pushCall(abi.FuncPCABI0(asyncPreempt), newpc)
		}
	}

	// Acknowledge the preemption.
	gp.m.preemptGen.Add(1)
	gp.m.signalPending.Store(0)

	if GOOS == "darwin" || GOOS == "ios" {
		pendingPreemptSignals.Add(-1)
	}
}

const preemptMSupported = true

// preemptM sends a preemption request to mp. This request may be
// handled asynchronously and may be coalesced with other requests to

	// 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
}

	}
	return n
}

// nosplit to avoid preemption or morestack spilling registers.
//
//go:nosplit
//go:noinline
func testTracebackArgs10(a, b, c, d, e int32) int {
	// no use of any args
	return runtime.Stack(testTracebackArgsBuf[:], false)
}

// norace to avoid race instrumentation changing spill locations.
// nosplit to avoid preemption or morestack spilling registers.
//
//go:norace

		},
	)
	PreemptionVictims = metrics.NewHistogram(
		&metrics.HistogramOpts{
			Subsystem: SchedulerSubsystem,
			Name:      "preemption_victims",
			Help:      "Number of selected preemption victims",
			// we think #victims>64 is pretty rare, therefore [64, +Inf) is considered a single bucket.
			Buckets:        metrics.ExponentialBuckets(1, 2, 7),
			StabilityLevel: metrics.STABLE,
		})

	// 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