elektron/schedulers/schedPolicy.go

package schedulers

import (
	"bitbucket.org/sunybingcloud/electron/def"
	mesos "github.com/mesos/mesos-go/api/v0/mesosproto"
	sched "github.com/mesos/mesos-go/api/v0/scheduler"
)

type SchedPolicyContext interface {
	// Change the state of scheduling.
	SwitchSchedPol(s SchedPolicyState)
}

type SchedPolicyState interface {
	// Define the particular scheduling policy's methodology of resource offer consumption.
	ConsumeOffers(SchedPolicyContext, sched.SchedulerDriver, []*mesos.Offer)
	// Get information about the scheduling policy.
	GetInfo() (info struct {
		taskDist    float64
		varCpuShare float64
	})
	// Switch scheduling policy if necessary.
	SwitchIfNecessary(SchedPolicyContext)
}

type baseSchedPolicyState struct {
	SchedPolicyState
	// Keep track of the number of tasks that have been scheduled.
	numTasksScheduled int
	// Distribution of tasks that the scheduling policy is most appropriate for.
	// This distribution corresponds to the ratio of low power consuming tasks to
	// high power consuming tasks.
	TaskDistribution float64 `json:"taskDist"`
	// The average variance in cpu-share per task that this scheduling policy can cause.
	// Note: This number corresponds to a given workload.
	VarianceCpuSharePerTask float64 `json:"varCpuShare"`
}

func (bsps *baseSchedPolicyState) SwitchIfNecessary(spc SchedPolicyContext) {
	baseSchedRef := spc.(*BaseScheduler)
	// Switching scheduling policy only if feature enabled from CLI
	if baseSchedRef.schedPolSwitchEnabled {
		// Name of the scheduling policy to switch to.
		switchToPolicyName := ""
		// Need to recompute size of the scheduling window for the next offer cycle.
		// The next scheduling policy will schedule at max schedWindowSize number of tasks.
		baseSchedRef.schedWindowSize, baseSchedRef.numTasksInSchedWindow =
			baseSchedRef.schedWindowResStrategy.Apply(func() interface{} { return baseSchedRef.tasks })
		// Determine the distribution of tasks in the new scheduling window.
		taskDist, err := def.GetTaskDistributionInWindow(baseSchedRef.schedWindowSize, baseSchedRef.tasks)
		// If no resource offers have been received yet, and
		// 	the name of the first scheduling policy to be deployed is provided,
		// 	we switch to this policy regardless of the task distribution.
		if !baseSchedRef.hasReceivedResourceOffers && (baseSchedRef.nameOfFstSchedPolToDeploy != "") {
			switchToPolicyName = baseSchedRef.nameOfFstSchedPolToDeploy
		} else if err != nil {
			// All the tasks in the window were only classified into 1 cluster.
			// Max-Min and Max-GreedyMins would work the same way as Bin-Packing for this situation.
			// So, we have 2 choices to make. First-Fit or Bin-Packing.
			// If choose Bin-Packing, then there might be a performance degradation due to increase in
			// 	resource contention. So, First-Fit might be a better option to cater to the worst case
			// 	where all the tasks are power intensive tasks.
			// TODO: Another possibility is to do the exact opposite and choose Bin-Packing.
			// TODO[2]: Determine scheduling policy based on the distribution of tasks in the whole queue.
			switchToPolicyName = bp
		} else {
			// The tasks in the scheduling window were classified into 2 clusters, meaning that there is
			// 	some variety in the kind of tasks.
			// We now select the scheduling policy which is most appropriate for this distribution of tasks.
			first := schedPoliciesToSwitch[0]
			last := schedPoliciesToSwitch[len(schedPoliciesToSwitch)-1]
			if taskDist < first.sp.GetInfo().taskDist {
				switchToPolicyName = first.spName
			} else if taskDist > last.sp.GetInfo().taskDist {
				switchToPolicyName = last.spName
			} else {
				low := 0
				high := len(schedPoliciesToSwitch) - 1
				for low <= high {
					mid := (low + high) / 2
					if taskDist < schedPoliciesToSwitch[mid].sp.GetInfo().taskDist {
						high = mid - 1
					} else if taskDist > schedPoliciesToSwitch[mid].sp.GetInfo().taskDist {
						low = mid + 1
					} else {
						switchToPolicyName = schedPoliciesToSwitch[mid].spName
						break
					}
				}
				// We're here if low == high+1.
				// If haven't yet found the closest match.
				if switchToPolicyName == "" {
					lowDiff := schedPoliciesToSwitch[low].sp.GetInfo().taskDist - taskDist
					highDiff := taskDist - schedPoliciesToSwitch[high].sp.GetInfo().taskDist
					if lowDiff > highDiff {
						switchToPolicyName = schedPoliciesToSwitch[high].spName
					} else if highDiff > lowDiff {
						switchToPolicyName = schedPoliciesToSwitch[low].spName
					} else {
						// index doens't matter as the values at high and low are equidistant
						// 	from taskDist.
						switchToPolicyName = schedPoliciesToSwitch[high].spName
					}
				}
			}
		}
		// Switching scheduling policy.
		baseSchedRef.LogSchedPolicySwitch(taskDist, switchToPolicyName, SchedPolicies[switchToPolicyName])
		baseSchedRef.SwitchSchedPol(SchedPolicies[switchToPolicyName])
		// Resetting the number of tasks scheduled.
		bsps.numTasksScheduled = 0
	}
}

func (bsps *baseSchedPolicyState) GetInfo() (info struct {
	taskDist    float64
	varCpuShare float64
}) {
	info.taskDist = bsps.TaskDistribution
	info.varCpuShare = bsps.VarianceCpuSharePerTask
	return info
}