nova schedule 排程器之FilterSchedulerz中的 get_weighed_hosts

在filter_scheduler.py 的_schedule 中會調用get_weighed_hosts 來為host計算權重

  weighed_hosts = self.host_manager.get_weighed_hosts(hosts,spec_obj)

具體實作在host_manager.py的HostManager 類中

 def get_weighed_hosts(self, hosts, spec_obj):

        """Weigh the hosts."""

        return self.weight_handler.get_weighed_objects(self.weighers,

                hosts, spec_obj)

get_weighed_objects 的實作在nova/weights.py 中

class BaseWeightHandler(loadables.BaseLoader):

    object_class = WeighedObject

    def get_weighed_objects(self, weighers, obj_list, weighing_properties):

        """Return a sorted (descending), normalized list of WeighedObjects."""

        weighed_objs = [self.object_class(obj, 0.0) for obj in obj_list]

        if len(weighed_objs) <= 1:

            return weighed_objs

        for weigher in weighers:

            weights = weigher.weigh_objects(weighed_objs, weighing_properties)

            # Normalize the weights

            weights = normalize(weights,

                                minval=weigher.minval,

                                maxval=weigher.maxval)

            for i, weight in enumerate(weights):

                obj = weighed_objs[i]

                obj.weight += weigher.weight_multiplier() * weight

//将個個權重計算出來後，再進行排序，看起來還是逆序的

        return sorted(weighed_objs, key=lambda x: x.weight, reverse=True)

最關鍵的一句是調用weigh_objects，這個同樣在nova/weights.py 中的BaseWeigher 類中

    def weigh_objects(self, weighed_obj_list, weight_properties):

        """Weigh multiple objects.

        Override in a subclass if you need access to all objects in order

        to calculate weights. Do not modify the weight of an object here,

        just return a list of weights.

        """

        # Calculate the weights

        weights = []

        for obj in weighed_obj_list:

            weight = self._weigh_object(obj.obj, weight_properties)

            weights.append(weight)

        return weights

在weigh_objects 中又調用_weigh_object，這就回到了schedule/weights 中的__init__.py中的

class BaseHostWeigher(weights.BaseWeigher):

    """Base class for host weights."""

    pass

這個是個空函數，但是卻是weights.BaseWeigher的子類，是以要實作對host的權重的計算必須是BaseHostWeigher的子類且實作了_weigh_object。這裡以disk.py 為例看看如果計算權重

class DiskWeigher(weights.BaseHostWeigher):

    minval = 0

    def weight_multiplier(self):

        """Override the weight multiplier."""

        return CONF.disk_weight_multiplier

    def _weigh_object(self, host_state, weight_properties):

        """Higher weights win.  We want spreading to be the default."""

        return host_state.free_disk_mb

原來就是直接傳回系統剩餘的disk 啊host_state.free_disk_mb