PFC

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It is supported to manage PFC with templates or with customized configurations.

Templated PFC Management By default, a default PFC threshold template exists in the system that supports globally enabling PFC for up to two queues. PFC for queues 3 and 4 has been enabled by default. Run show pfc profiles command to display the default PFC threshold configuration.
Customized PFC Management Configure a custom PG buffer profile to specify the PFC threshold. The specific steps for configuration are as follows:

Run priority-flow-control enable ingress-queue-id command to enable PFC for the queue globally.
Run buffer-profile buffer_profile_name command to create a lossless buffer profile.
Run class-map class_map_name command to create a class map to specify the queue.
Run policy-map policy_map_name command to create a policy map, and run class class_map_name to bind it to the class map. Then run priority-group-buffer buffer_profile_name command to bind to the priority-group buffer profile.
Run service-policy policy_map_name command to apply the policy to the interface. Due to the complexity of custom PFC configuration, it is recommended to use default template PFC in preference.

Table 1 PFC View

Command	Purpose
show interface priority-flow-control	Display the PFC status of interfaces.
show counters priority-flow-control	Display PFC counters.
clear counters priority-flow-control	Clear PFC counters.
show pfc profiles	Display PFC profiles.

show interface priority-flow-control

[Command] show interface priority-flow-control

[Purpose] Display the PFC status of interfaces.

[View] Privileged User View

[Use Cases]

sonic# show interface priority-flow-control
Interface    Lossless priorities
-----------  ---------------------
0/0          3,4
0/4          3,4
0/8          3,4
0/12         3,4
0/16         3,4
0/20         3,4
0/24         3,4
0/28         3,4
0/32         3,4
0/36         3,4
0/40         3,4
0/44         3,4
0/48         3,4
0/52         3,4
0/56         3,4
0/60         3,4
0/64         3,4
0/68         3,4
0/72         3,4
0/76         3,4
0/80         3,4
0/84         3,4
0/88         3,4
0/92         3,4
0/96         3,4
0/100        3,4
0/104        3,4
0/108        3,4
0/112        3,4
0/116        3,4
0/120        3,4
0/124        3,4
0/128        3,4
0/129        3,4

show counters priority-flow-control

[Command] show counters priority-flow-control

[Purpose] Display PFC counters.

[View] Privileged User View

[Use Cases]

sonic# show counters priority-flow-control
      Port Rx    PFC0    PFC1    PFC2    PFC3    PFC4    PFC5    PFC6    PFC7
-----------  ------  ------  ------  ------  ------  ------  ------  ------
        0/0       0       0       0       0       0       0       0       0
        0/4       0       0       0       0       0       0       0       0
        0/8       0       0       0       0       0       0       0       0
       0/12       0       0       0       0       0       0       0       0
       0/16       0       0       0       0       0       0       0       0
       0/20       0       0       0       0       0       0       0       0
       0/24       0       0       0       0       0       0       0       0
       0/28       0       0       0       0       0       0       0       0
       0/32       0       0       0       0       0       0       0       0
       0/36       0       0       0       0       0       0       0       0
       0/40       0       0       0       0       0       0       0       0
       0/44       0       0       0       0       0       0       0       0
       0/48       0       0       0       0       0       0       0       0
       0/52       0       0       0       0       0       0       0       0
       0/56       0       0       0       0       0       0       0       0
       0/60       0       0       0       0       0       0       0       0
       0/64       0       0       0       0       0       0       0       0
       0/68       0       0       0       0       0       0       0       0
       0/72       0       0       0       0       0       0       0       0
       0/76       0       0       0       0       0       0       0       0
       0/80       0       0       0       0       0       0       0       0
       0/84       0       0       0       0       0       0       0       0
       0/88       0       0       0       0       0       0       0       0
       0/92       0       0       0       0       0       0       0       0
       0/96       0       0       0       0       0       0       0       0
      0/100       0       0       0       0       0       0       0       0
      0/104       0       0       0       0       0       0       0       0
      0/108       0       0       0       0       0       0       0       0
      0/112       0       0       0       0       0       0       0       0
      0/116       0       0       0       0       0       0       0       0
      0/120       0       0       0       0       0       0       0       0
      0/124       0       0       0       0       0       0       0       0
      0/128       0       0       0       0       0       0       0       0
      0/129       0       0       0       0       0       0       0       0
    Port Tx    PFC0    PFC1    PFC2    PFC3    PFC4    PFC5    PFC6    PFC7
-----------  ------  ------  ------  ------  ------  ------  ------  ------
        0/0       0       0       0       0       0       0       0       0
        0/4       0       0       0       0       0       0       0       0
        0/8       0       0       0       0       0       0       0       0
       0/12       0       0       0       0       0       0       0       0
       0/16       0       0       0       0       0       0       0       0
       0/20       0       0       0       0       0       0       0       0
       0/24       0       0       0       0       0       0       0       0
       0/28       0       0       0       0       0       0       0       0
       0/32       0       0       0       0       0       0       0       0
       0/36       0       0       0       0       0       0       0       0
       0/40       0       0       0       0       0       0       0       0
       0/44       0       0       0       0       0       0       0       0
       0/48       0       0       0       0       0       0       0       0
       0/52       0       0       0       0       0       0       0       0
       0/56       0       0       0       0       0       0       0       0
       0/60       0       0       0       0       0       0       0       0
       0/64       0       0       0       0       0       0       0       0
       0/68       0       0       0       0       0       0       0       0
       0/72       0       0       0       0       0       0       0       0
       0/76       0       0       0       0       0       0       0       0
       0/80       0       0       0       0       0       0       0       0
       0/84       0       0       0       0       0       0       0       0
       0/88       0       0       0       0       0       0       0       0
       0/92       0       0       0       0       0       0       0       0
       0/96       0       0       0       0       0       0       0       0
      0/100       0       0       0       0       0       0       0       0
      0/104       0       0       0       0       0       0       0       0
      0/108       0       0       0       0       0       0       0       0
      0/112       0       0       0       0       0       0       0       0
      0/116       0       0       0       0       0       0       0       0
      0/120       0       0       0       0       0       0       0       0
      0/124       0       0       0       0       0       0       0       0
      0/128       0       0       0       0       0       0       0       0
      0/129       0       0       0       0       0       0       0       0

clear counters priority-flow-control

[Command] clear counters priority-flow-control

[Purpose] Clear PFC counters.

[View] Privileged User View

[Use Cases]

sonic# clear counters priority-flow-control

show pfc profiles

[Command] show pfc profiles

[Purpose] Display PFC profiles.

[View] Privileged User View

[Use Cases]

sonic# show pfc profile
{
    "ingress_lossless_profile":{
        "dynamic_th":"1",
        "pool":"ingress_lossless_pool",
        "size":"1518",
        "xoff":"38816",
        "xon_offset":"13440"
    },
    "pg_lossless_1":{
        "dynamic_th":"-4",
        "pool":"ingress_lossless_pool",
        "size":"1518",
        "xoff":"46496",
        "xon_offset":"13440"
    },
    "pg_lossless_100000_40m_profile":{
        "dynamic_th":"1",
        "pool":"ingress_lossless_pool",
        "size":"1518",
        "xoff":"38816",
        "xon":"0",
        "xon_offset":"13440"
}
}

PFC Config

Table 2 PFC Config

Command	Purpose
priority-flow-control enable ingress-queue-id	Globally enable PFC for the queue.
buffer-profile buffer_profile_name	Configure a custom PFC buffer profile and enter Buffer Configuration View.
mode lossless {static static_th\|dynamic dynamic_th} size size	Set a PFC lossless buffer. (For CX308P-48Y-N-V2, CX532P-N-V2 and CX732Q-N-V2)
mode lossless {static static_th\|dynamic dynamic_th} size size xoff xoff xon-offset xon-offset [xon xon]	Set a PFC lossless buffer. (For other models)
priority-group-buffer buffer_profile_name	Bind the PG buffer profile to the queue at ingress.

priority-flow-control enable

[Command] priority-flow-control enable ingress-queue-id

[Purpose] Globally enable PFC for the queue.

[Parameters]

Parameter	Description
ingress-queue-id	Queue ID, the range is [0,7]

[View] Global Configuration View

[Notes] Only support up to two queues to enable PFC globally, by default, PFC of queue 3, 4 have been enabled. If you want to enable PFC for other queues, please disable PFC of queue 3 or 4 first. Configuring the PFC global enable queue requires reload to take effect. Port-based modification of PFC enable queues is not supported at this time. Run command no priority-flow-control enable ingress-queue-id to disable PFC for the queue.

[Use Cases]

sonic# configure
sonic(config)# priority-flow-control enable 4

buffer-profile

[Command] buffer-profile buffer_profile_name

[Purpose] Configure a custom PFC buffer profile and enter Buffer Configuration View.

[Parameters]

Parameter	Description
buffer_profile_name	Profile name.

[View] Global Configuration View

[Notes] Run command no buffer-profile profile_name to delete the buffer profile.

[Use Cases]

sonic(config)# buffer-profile testname
sonic(config-buffer-profile-testname)#

mode lossless {static

[Command] mode lossless {static static_th|dynamic dynamic_th} size size

[Purpose] Set a PFC lossless buffer. (For CX308P-48Y-N-V2, CX532P-N-V2 and CX732Q-N-V2)

[Parameters]

Parameter	Description
static_th	Set the static threshold value in bytes. This parameter is meaningless on CX308P-48Y-N-V2, CX532P-N-V2 and CX732Q-N-V2, and should be configured as 0.
dynamic_th	Set the dynamic threshold value in integer. The value shall not be less than -5. Dynamic threshold = (dynamic_th + 6) * remaining available buffer on CX308P-48Y-N-V2, CX532P-N-V2 and CX732Q-N-V2. For example, if dynamic_th is set to -4, the dynamic threshold is 2 times the remaining available buffer;
size	Set the guaranteed buffer in bytes. It is recommended to be an integer multiple of the cell size. The recommended configuration value is 25600.

[View] Buffer Configuration View

[Notes]

**INFO: **The cell size varies by model. On CX308P-48Y-N-V2, CX532P-N-V2 and CX732Q-N-V2, the cell size is 128 Bytes. On CX864E-N, the cell size is 512 Bytes. On other models, the cell size is 224 bytes.

When congestion occurs at a queue and the ingress buffer occupancy reaches the watermark, it starts sending pause frames. When the sender receives a pause frame and reduces the traffic sent, the ingress buffer occupancy of the switch decreases and stops sending pause frames when the occupancy falls below the watermark. The formula for calculating the PFC watermark is: Limit=Guaranteed Buffers + Dynamic Factor. Dynamic Factor is 0 in static mode. The sum of the lossless buffers allocated to each queue shall be no greater than the lossless pool size. Recommended Configuration:

!
buffer-profile lossless_buffer_profile
 mode lossless dynamic -3 size 0

[Use Cases]

sonic(config)# buffer-profile buffer_test
sonic(config-buffer-profile-buffer_test)# mode lossless dynamic -3 size 0

mode lossless {static

[Command] mode lossless {static static_th|dynamic dynamic_th} size size xoff xoff xon-offset xon-offset [xon xon]

[Purpose] Set a PFC lossless buffer. (For other models)

[Parameters]

Parameter	Description
static_th	Set the static threshold value in bytes. The range is from 0 to 47218432.
dynamic_th	Set the dynamic threshold value in integer. The range is from -4 to 3. Dynamic threshold = 2dynamic_th * remaining available buffer. For example, if dynamic_th is set to 1, then dynamic threshold is two times the remaining available buffer, that is, the actual threshold is two-thirds of the total available buffer.
size	Set the guaranteed buffer in bytes. The recommended value is 1518.
xoff	Set PFC pause frame trigger cache threshold value in bytes, which is recommended to be an integer multiple of the cell size. Xoff is related to cable length, port speed and so on, you may refer to the recommended values below to configure. Xoff value must be greater than xon value.
xon-offset	Set PFC pause frame stop buffer threshold value in bytes, it is recommended to be an integer multiple of cell size. The recommended value is 13440.
xon	(Optional) It should be an integer multiple of cell size and the unit is byte. It is recommended to configure 0, since the actual xon takes the larger value of xon and xon-offset, so it is generally not necessary to set the value of xon.

The parameters of dynamic lossless buffer are related to the port speed, cable length, etc. The following are the recommended values:

[View] Buffer Configuration View

[Notes] When congestion occurs at a queue and the ingress buffer occupancy reaches xoff, it starts sending pause frames. When the sender receives pause frames and reduces the traffic sent, the ingress buffer occupancy of the switch decreases and stops sending pause frames when the occupancy reaches xon. The default ingress pause frame trigger threshold and pause frame stop threshold exist in the interface configuration when not configured by the user. The sum of the lossless buffers allocated to each queue shall be no greater than the lossless pool size.

hint{type=“warning”} **Warning: **The parameters of dynamic lossless buffer are related to the port speed, cable length, etc. We recommend you to use “Easy RoCE” to automatically generate lossless parameters. Improper configuration may cause packet loss during traffic transmission.

If you want to assign them manually, the following are recommended parameters for different speeds interfaces.

Recommended configurations for the CX864E-N model:

port speed	cable length	size	xoff	dynamic threshold	xon_offset
25000	5m	1518	15680	1	9408
50000	5m	1518	21248	1	9408
100000	5m	1518	34624	1	9408
200000	5m	1518	62368	1	9408
400000	5m	1518	117536	1	9408
800000	5m	1518	197536	1	9408
25000	40m	1518	16928	1	9408
50000	40m	1518	23392	1	9408
100000	40m	1518	38816	1	9408
200000	40m	1518	71904	1	9408
400000	40m	1518	135520	1	9408
800000	40m	1518	205520	1	9408
25000	100m	1518	18848	1	9408
50000	100m	1518	27264	1	9408
100000	100m	1518	46496	1	9408
200000	100m	1518	87168	1	9408
400000	100m	1518	166688	1	9408
800000	100m	1518	236688	1	9408
25000	300m	1518	25184	1	9408
50000	300m	1518	40128	1	9408
100000	300m	1518	72384	1	9408
200000	300m	1518	138112	1	9408
400000	300m	1518	268640	1	9408
800000	300m	1518	468640	1	9408

Recommended configurations for other models:

port speed	cable length	size	xoff	dynamic threshold	xon_offset
25000	5m	1518	15680	1	13440
50000	5m	1518	21248	1	13440
100000	5m	1518	34624	1	13440
200000	5m	1518	62368	1	13440
400000	5m	1518	117536	1	13440
25000	40m	1518	16928	1	13440
50000	40m	1518	23392	1	13440
100000	40m	1518	38816	1	13440
200000	40m	1518	71904	1	13440
400000	40m	1518	135520	1	13440
25000	100m	1518	18848	1	13440
50000	100m	1518	27264	1	13440
100000	100m	1518	46496	1	13440
200000	100m	1518	87168	1	13440
400000	100m	1518	166688	1	13440
25000	300m	1518	25184	1	13440
50000	300m	1518	40128	1	13440
100000	300m	1518	72384	1	13440
200000	300m	1518	138112	1	13440
400000	300m	1518	268640	1	13440

[Use Cases]

sonic(config)# buffer-profile pg_lossless_100000_100m_profile
sonic(config-buffer-profile-pg_lossless_100000_100m_profile)# mode lossless dynamic 1 size 1518 xoff 46496 xon-offset 13440

priority-group-buffer

[Command] priority-group-buffer buffer_profile_name

[Purpose] Bind the PG buffer profile to the queue at ingress.

[Parameters]

Parameter	Description
buffer_profile_name	Profile name.

[View] Policy Map-Class Map Configuration View

[Notes] Please bind an existing class map to specify the queue for policy matching, and the queue should be globally PFC-enabled. Run command no priority-group-buffer buffer_profile_name to unbind the PG buffer profile.

[Use Cases]

sonic(config)# buffer-profile pg_lossless_100000_100m_profile
sonic(config-buffer-profile-pg_lossless_100000_100m_profile)# mode lossless dynamic 1 size 1518 xoff 46496 xon-offset 13440
sonic(config-buffer-profile-pg_lossless_100000_100m_profile)# exit
sonic(config)# polic-map test1
sonic(config-pmap-test1)# class cmap_4
sonic(config-pmap-c)# priority-group-buffer pg_lossless_100000_100m_profile