Mellanox MLNX-OS User Manual for SX1018HP Ethernet Managed Blade Switch

Rev 2.10
Mellanox Technologies
499
Mellanox Technologies Confidential
5.9 Quality of Service (QoS)
5.9.1 Priority Flow Control and Link Level Flow Control
Priority Flow Control (PFC) provides an enhancement to the existing pause mechanism in Ether-
net. The current Ethernet pause option stops all traf
fic on a link. PFC creates eight separate vir-
tual links on the physical link and allows any of these links to
be paused and restarted
independently, enabling the network to create a no-drop class of service for an individual virtual
link. PFC has 8 possible priorities (3 bits in VLAN header). Each priority can be mapped to one
of 4 possible queues in the ingress.
The PFC software offers the foll
owing features:
• Provides per-priority enabling or disabling of flow control
• Transmits PFC-PAUSE frames when the receive threshold for a particular traffic class is
reac
hed
• Provides the management capability for
an administrator to configure the flow control
properties on each port of the switch
• Keeps flow control disabled for all priorities on all
ports by default
• Allows an administrator to enable or disable flow control per port and per priority level
• Supports flow control only on physical ports, not on logical interfaces such as tunnels or
interfaces
defined by sharing a physical port in multiple virtual switch contexts
• Uses the configured threshold values to set up the que
ue buffer spaces accordingly in
the datapath
• Provides hardware abst
raction layer callouts for the following:
• Enabling or disabling of flow control on each port for eac
h priority
• Configuring the queue depth for each priority on each port
• Supports MIB defined in the 802.1Qbb standard and a proprietary MIB for management
• Provides trace logs for execution upon error conditions and for any event noti
fications
from the hardware or datapath. These trace logs are a useful aid in troubleshooting.
• Allows the administrator to co
nfigure the minimum and maximum threshold values for
flow control. These configurations are applied globally on all ports and priorities.
Priority Based Flow Control (PFC) provides an enha
ncement to the existing pause flow control
mechanism as described in 802.1X.
 To enable PFC globally:
Step 1. Log in as admin.
Step 2. Enter config mode. Run:
Step 3. Enable PFC globally on the switch. Run:
switch > enable
switch # configure terminal
switch (config) # dcb priority-flow-control enable
This action might cause traffic loss while shutting down a port with priority-flow-con-
trol mode on
Type 'yes' to confirm enable pfc globally: yes