Here is more detailed link
http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/sw/qos/Cisco_Nexus_5000_Series_NX-OS_Quality_of_Service_Configuration_Guide_chapter3.html#task_1135199
Please read carefuly docimentation on QoS before doing any confguration on the device.
The following predefined policy maps are used as default service policies:
Type network qos policies can only be configured on the system qos attachment point. They are applied to the entire switch for a particular class
Type queuing policies are used for scheduling and buffering the traffic of a specific system class. A type queuing policy is identified by its qos-group and can be attached to the system or to individual interfaces (except for Fabric Extender host interfaces) for input or output traffic.
Type qos policies are used for classifying the traffic of a specific system class identified by a unique qos-group value. A type qos policy can be attached to the system or to individual interfaces (including Fabric Extender host interfaces) for input traffic only.
So following lines matches traffic marked with certain qos-group to system defined class-maps:
!maps traffic with qos group 1 to default class "class-fcoe"
class-map type queuing class-fcoe
match qos-group 1
!maps traffic with qos group 2 to default class "class-all-flood"
class-map type queuing class-all-flood
match qos-group 2
class-map type queuing class-ip-multicast
match qos-group 2
class-map type network-qos class-fcoe
match qos-group 1
class-map type network-qos class-all-flood
match qos-group 2
class-map type network-qos class-ip-multicast
match qos-group 2
system qos - section where system qos policies are configured - they are applied to all interfaces by default
!lower you can see system policies
!applies qos (marking) policy-map for input - this will affect all interfaces by default
service-policy type qos input fcoe-default-in-policy
!applies queuing policy on icomming traffic
service-policy type queuing input fcoe-default-in-policy
!applies queuing policy on outgoint traffic
service-policy type queuing output fcoe-default-out-policy
!network qos policy applied to entire switch
service-policy type network-qos fcoe-default-nq-policy
Basically standart policy structure is
!creating class to which we will map traffic which falls in certain criteria
class map type X CLASS_NAME
!some criteria (ip address, protocol, cos)
match CRITERIA
!creating policy map which will MODIFY some traffic flow characteristics
policy-map type Y POLICY_NAME
!configuring class-map under policy maps meaning that this policy map will apply to all traffic matched by thic class-map
class CLASS_NAME
!applying changes
bandwidth ...
etc..
