nova schedule

在nova/schedule 中的rpcapi.py中接收别的模块发送过来的请求
def select_destinations(self, ctxt, spec_obj):
        version = '4.3'
        msg_args = {'spec_obj': spec_obj}
        if not self.client.can_send_version(version):
            del msg_args['spec_obj']
            msg_args['request_spec'] = spec_obj.to_legacy_request_spec_dict()
            msg_args['filter_properties'
                     ] = spec_obj.to_legacy_filter_properties_dict()
            version = '4.0'
        cctxt = self.client.prepare(version=version)
        return cctxt.call(ctxt, 'select_destinations', **msg_args)
这个函数又通过cctxt.call(ctxt, 'select_destinations', **msg_args) 调用到manage.py中
 def select_destinations(self, ctxt,
                            request_spec=None, filter_properties=None,
                            spec_obj=_sentinel):
        """Returns destinations(s) best suited for this RequestSpec.

        The result should be a list of dicts with 'host', 'nodename' and
        'limits' as keys.
        """

        # TODO(sbauza): Change the method signature to only accept a spec_obj
        # argument once API v5 is provided.
        if spec_obj is self._sentinel:
            spec_obj = objects.RequestSpec.from_primitives(ctxt,
                                                           request_spec,
                                                           filter_properties)
        dests = self.driver.select_destinations(ctxt, spec_obj)
        return jsonutils.to_primitive(dests)
其中self.driver 是在SchedulerManager.init 中赋值
def __init__(self, scheduler_driver=None, *args, **kwargs):
        if not scheduler_driver:
            scheduler_driver = CONF.scheduler_driver
        try:
            self.driver = driver.DriverManager(
                    "nova.scheduler.driver",
                    scheduler_driver,
                    invoke_on_load=True).driver
这个driver的基类是driver.py其有两个子类filter_scheduler.py 和 chance.py 默认使用filter_scheduler.py
class FilterScheduler(driver.Scheduler)也可以证明FilterScheduler 是driver.Scheduler的子类
 def select_destinations(self, context, spec_obj):
        """Selects a filtered set of hosts and nodes."""
        self.notifier.info(
            context, 'scheduler.select_destinations.start',
            dict(request_spec=spec_obj.to_legacy_request_spec_dict()))

        num_instances = spec_obj.num_instances
        selected_hosts = self._schedule(context, spec_obj)

        # Couldn't fulfill the request_spec
        if len(selected_hosts) < num_instances:
            # NOTE(Rui Chen): If multiple creates failed, set the updated time
            # of selected HostState to None so that these HostStates are
            # refreshed according to database in next schedule, and release
            # the resource consumed by instance in the process of selecting
            # host.
            for host in selected_hosts:
                host.obj.updated = None

            # Log the details but don't put those into the reason since
            # we don't want to give away too much information about our
            # actual environment.
            LOG.debug('There are %(hosts)d hosts available but '
                      '%(num_instances)d instances requested to build.',
                      {'hosts': len(selected_hosts),
                       'num_instances': num_instances})

            reason = _('There are not enough hosts available.')
            raise exception.NoValidHost(reason=reason)

        dests = [dict(host=host.obj.host, nodename=host.obj.nodename,
                      limits=host.obj.limits) for host in selected_hosts]

        self.notifier.info(
            context, 'scheduler.select_destinations.end',
            dict(request_spec=spec_obj.to_legacy_request_spec_dict()))
        return dests

select_destinations 首先调用FilterScheduler.Scheduler来选择host
selected_hosts = self._schedule(context, spec_obj)
最后通过rpc发送消息
self.notifier.info(
            context, 'scheduler.select_destinations.end',
            dict(request_spec=spec_obj.to_legacy_request_spec_dict()))
notifier的赋值也是在FilterScheduler的init函数中
self.notifier = rpc.get_notifier('scheduler')
schedule的主要工作在FilterScheduler的_schedule 函数中，会通过filter和weight 来选择不同的host.