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Add DSCP resolution from TC in packet trim #2155

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Merged
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Apr 10, 2025
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Add DSCP resolution from TC in packet trim #2155

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48 changes: 48 additions & 0 deletions doc/SAI-Proposal-Packet-Trimming.md
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Original file line number Diff line number Diff line change
Expand Up @@ -164,3 +164,51 @@ Both the queue and the port have the packet counter to reflect the number of tri
/** Packets trimmed due to failed admission [uint64_t] */
SAI_QUEUE_STAT_TRIM_PACKETS = 0x00000028,
```

It can also be beneficial to support multiple DSCP values for trimmed packets sent out via different ports. For example, trimmed packets sent to hosts will get DSCP 5 whereas trimmed packets sent to uplink/spine will have DSCP 7. It is to allow to the destination NIC to know where congestion happened - on downlinks to servers or in the fabric. Such information can be used for a better decision making on how to react to the state of network.

![](figures/trim-TC.png)

The diagram above shows the general concept - instead of setting a trim DSCP, we set a trim TC value, which, by applying a different TC to DSCP map per egres port, will yield a different DSCP value.

```
typedef enum _sai_packet_trim_dscp_resolution_mode_t
{
/**
* @brief Static DSCP resolution.
*
* In this mode, a new DSCP for the trimmed packet is set directly
* by the application.
*/
SAI_PACKET_TRIM_DSCP_RESOLUTION_MODE_DSCP_VALUE,

/**
* @brief Dynamic DSCP resolution.
*
* In this mode, a new DSCP for the trimmed packet is resolved from the new TRIM_TC
* set by the application using per-port TC_TO_DSCP mapping
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@bandaru-viswanath bandaru-viswanath Mar 24, 2025 •
edited
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The saiqosmap.h defines only TC_AND_COLOR_TO_DSCP map, but no TC_TO_DSCP map, as part of the set of valid qos maps. In this case, a color value also need to be supplied if this mechanism is desired. Could you please clarify ?

SAI_QOS_MAP_TYPE_TC_AND_COLOR_TO_DSCP = 0x00000005,

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@marian-pritsak marian-pritsak Mar 25, 2025

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Color does not need to be supplied. The user can just map all the colors to same DSCP, since the TC is used for trimming.

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@bandaru-viswanath bandaru-viswanath Apr 8, 2025

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Or is it possible that different-colors are mapped to different DSCP values ? Is this a valid configuration ?

*/
SAI_PACKET_TRIM_DSCP_RESOLUTION_MODE_FROM_TC
} sai_packet_trim_dscp_resolution_mode_t;
```

```
/**
* @brief New packet trim TC value
*
* @type sai_uint8_t
* @flags CREATE_AND_SET
* @default 0
* @validonly SAI_SWITCH_ATTR_PACKET_TRIM_DSCP_RESOLUTION_MODE == SAI_PACKET_TRIM_DSCP_RESOLUTION_MODE_FROM_TC
*/
SAI_SWITCH_ATTR_PACKET_TRIM_TC_VALUE,

/**
* @brief DSCP mapping mode for a trimmed packet
*
* @type sai_packet_trim_dscp_resolution_mode_t
* @flags CREATE_AND_SET
* @default SAI_PACKET_TRIM_DSCP_RESOLUTION_MODE_DSCP_VALUE
*/
SAI_SWITCH_ATTR_PACKET_TRIM_DSCP_RESOLUTION_MODE,
```
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39 changes: 39 additions & 0 deletions inc/saiswitch.h
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Original file line number Diff line number Diff line change
Expand Up @@ -640,6 +640,25 @@ typedef enum _sai_packet_trim_queue_resolution_mode_t

} sai_packet_trim_queue_resolution_mode_t;

typedef enum _sai_packet_trim_dscp_resolution_mode_t
{
/**
* @brief Static DSCP resolution.
*
* In this mode, a new DSCP for the trimmed packet is set directly
* by the application.
*/
SAI_PACKET_TRIM_DSCP_RESOLUTION_MODE_DSCP_VALUE,

/**
* @brief Dynamic DSCP resolution.
*
* In this mode, a new DSCP for the trimmed packet is resolved from the new TRIM_TC
* set by the application using per-port TC_TO_DSCP mapping
*/
SAI_PACKET_TRIM_DSCP_RESOLUTION_MODE_FROM_TC
} sai_packet_trim_dscp_resolution_mode_t;

/**
* @brief Attribute Id in sai_set_switch_attribute() and
* sai_get_switch_attribute() calls.
Expand Down Expand Up @@ -3169,6 +3188,7 @@ typedef enum _sai_switch_attr_t
* @type sai_uint8_t
* @flags CREATE_AND_SET
* @default 0
* @validonly SAI_SWITCH_ATTR_PACKET_TRIM_DSCP_RESOLUTION_MODE == SAI_PACKET_TRIM_DSCP_RESOLUTION_MODE_DSCP_VALUE
*/
SAI_SWITCH_ATTR_PACKET_TRIM_DSCP_VALUE,

Expand Down Expand Up @@ -3277,6 +3297,25 @@ typedef enum _sai_switch_attr_t
*/
SAI_SWITCH_ATTR_SYNCE_CLOCK_LIST,

/**
* @brief New packet trim TC value
*
* @type sai_uint8_t
* @flags CREATE_AND_SET
* @default 0
* @validonly SAI_SWITCH_ATTR_PACKET_TRIM_DSCP_RESOLUTION_MODE == SAI_PACKET_TRIM_DSCP_RESOLUTION_MODE_FROM_TC
*/
SAI_SWITCH_ATTR_PACKET_TRIM_TC_VALUE,

/**
* @brief DSCP mapping mode for a trimmed packet
*
* @type sai_packet_trim_dscp_resolution_mode_t
* @flags CREATE_AND_SET
* @default SAI_PACKET_TRIM_DSCP_RESOLUTION_MODE_DSCP_VALUE
*/
SAI_SWITCH_ATTR_PACKET_TRIM_DSCP_RESOLUTION_MODE,

/**
* @brief End of attributes
*/
Expand Down
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