6 quality of service properties – Dell Mellanox Family of Adapters User Manual
Page 28
Driver Installation and Configuration
Rev 1.1
Mellanox Technologies
28
•
When the user uses
sk_prio
, it is mapped into a UP by the
‘tc’
tool. This is done by the
tc_wrap.py
tool which gets a list of <= 16 comma separated UP and maps the
sk_prio
to
the specified UP.
For example,
tc_wrap.py -ieth0 -u 1,5
maps
sk_prio 0
of
eth0
device to UP 1 and
sk_prio 1
to UP 5.
•
Setting
set_egress_map
in VLAN, maps the
skb_priority
of the VLAN to a
vlan_qos
.
The
vlan_qos
is represents a UP for the VLAN device.
•
In RoCE,
rdma_set_option
with
RDMA_OPTION_ID_TOS
could be used to set the UP
•
When creating QPs, the
sl
field in
ibv_modify_qp
command represents the UP
•
Indicating the TC
•
After mapping the
skb_priority
to UP, one should map the UP into a TC. This assigns
the user priority to a specific hardware traffic class. In order to do that,
mlnx_qos
should
be used.
mlnx_qos
gets a list of a mapping between UPs to TCs. For example,
mlnx_qos -
ieth0 -p 0,0,0,0,1,1,1,1
maps UPs 0-3 to
TC0
, and Ups 4-7 to
TC1
.
4.2.3.6 Quality of Service Properties
The different QoS properties that can be assigned to a TC are:
•
Strict Priority (see
•
Minimal Bandwidth Guarantee (ETS) (see
“Minimal Bandwidth Guarantee (ETS)”
•
Rate Limit (see
)
Strict Priority
When setting a TC's transmission algorithm to be 'strict', then this TC has absolute (strict) prior-
ity over other TC strict priorities coming before it (as determined by the TC number: TC 7 is
highest priority, TC 0 is lowest). It also has an absolute priority over non strict TCs (ETS).
This property needs to be used with care, as it may easily cause starvation of other TCs.
A higher strict priority TC is always given the first chance to transmit. Only if the highest strict
priority TC has nothing more to transmit, will the next highest TC be considered.
Non strict priority TCs will be considered last to transmit.
This property is extremely useful for low latency low bandwidth traffic. Traffic that needs to get
immediate service when it exists, but is not of high volume to starve other transmitters in the sys-
tem.
Minimal Bandwidth Guarantee (ETS)
After servicing the strict priority TCs, the amount of bandwidth (BW) left on the wire may be
split among other TCs according to a minimal guarantee policy.
If, for instance, TC0 is set to 80% guarantee and TC1 to 20% (the TCs sum must be 100), then
the BW left after servicing all strict priority TCs will be split according to this ratio.
Since this is a minimal guarantee, there is no maximum enforcement. This means, in the same
example, that if TC1 did not use its share of 20%, the reminder will be used by TC0.
Rate Limit
Rate limit defines a maximum bandwidth allowed for a TC. Please note that 10% deviation from
the requested values is considered acceptable.