Add packet trimming API

When a packet is lost, it can be recovered through fast retransmission (e.g., Go-Back-N in RoCE) or by using timeouts. Retransmission triggered by timeouts typically incurs significant latency. Packet trimming aims to facilitate rapid packet loss notification and, consequently, eliminate slow timeout-based retransmissions. Signed-off-by: Marian Pritsak <marianp@mellanox.com>
opencomputeproject · Oct 29, 2024 · 363bf8f · 363bf8f
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diff --git a/doc/SAI-Proposal-Packet-Trimming.md b/doc/SAI-Proposal-Packet-Trimming.md
@@ -0,0 +1,165 @@
+# Switch Abstraction Interface Change Proposal for Packet Trimming
+
+Title       | Packet Trimming
+------------|----------------
+Authors     | Nvidia
+Status      | In review
+Type        | Standards track
+Created     | 8/28/2024
+SAI-Version | 1.14
+----------
+
+## Overview
+When the lossy queue exceeds a buffer threshold, it drops packets without any notification to the destination host.
+
+When a packet is lost, it can be recovered through fast retransmission (e.g., Go-Back-N in RoCE) or by using timeouts. Retransmission triggered by timeouts typically incurs significant latency. Packet trimming aims to facilitate rapid packet loss notification and, consequently, eliminate slow timeout-based retransmissions.
+
+To help the host recover data more quickly and accurately, we introduce a packet trimming feature, that upon a failed packet admission to a shared buffer,
+will trim a packet to a configured size, and try sending it on a different queue to deliver a packet drop notification to an end host.
+
+```
+                                                                                                                                        
+                                                                                       ┌───────────────┐                                
+                                                                                       │               │                                
+                                                                                       │Trimmed packet │                                
+                                                                                       │               │                                
+                                                                                       └───────────────┘                                
+                                                                                                                                        
+                                                                                                    ┌─┬─┬─┬─┬────────┐                  
+                                                                                                    │ │ │ │ │        │                  
+                                                                                                    │ │ │ │ │        │                  
+                                                                                   ┌────────────────► │ │ │ │        │                  
+                                                                                   │                │ │ │ │ │        │    Queue         
+                                                                                   │                │ │ │ │ │        │                  
+                                                                                   │                │ │ │ │ │        │                  
+                                                                                   │                └─┴─┴─┴─┴────────┘                  
+     ┌──────────────┐                                                              │                                                    
+     │              │  ┌──────────────────────────────────────────────────────┐    │                ┌─┬─┬─┬─┬─┬─┬─┬─┬┐                  
+     │              │  │                                                      │    │                │ │ │ │ │ │ │ │ ││                  
+     │              │  │                                                      │    │     \   /      │ │ │ │ │ │ │ │ ││                  
+     │              │  │                                                      │    │      \ /       │ │ │ │ │ │ │ │ ││                  
+     │    Packet    │  │           Pipeline                                   ┼────┼───────\────────► │ │ │ │ │ │ │ ││     Queue        
+     │              │  │                                                      │           / \       │ │ │ │ │ │ │ │ ││                  
+     │              │  │                                                      │          /   \      │ │ │ │ │ │ │ │ ││                  
+     │              │  └──────────────────────────────────────────────────────┘                     └─┴─┴─┴─┴─┴─┴─┴─┴┘                  
+     │              │                                                                                                                   
+     │              │                                                                                                                   
+     │              │                                                                                                                   
+     └──────────────┘                                                                                                                   
+```
+
+This feature assumes that forwarding tables are configured properly, and the original packet would be delivered to the destination successfully if not for the congestion.
+
+## Spec
+There is a tradeoff between trying to configure a higher threshold in a queue buffer profile and trimming the packet.
+
+If the user chooses to configure higher thresholds for queues, the probability of a drop on a particular queue is lower only if other ports are less congested at the moment.
+
+However, if all the ports are equally utilized, it makes sense to create a different buffer profile for these queues, with a stricter threshold to have more fairness in shared buffer.
+
+A static trimming threshold may not be effective with shared buffer switches, where the buffer resources allocated to a queue or port can vary over time. Therefore, we propose adding a new attribute to a buffer profile to allow configuring packet trimming on such stricter profiles:
+```
+/**
+ * @brief Enum defining queue actions in case the packet fails to pass the admission control.
+ */
+typedef enum _sai_buffer_profile_packet_admission_fail_action_t
+{
+    /**
+     * @brief Drop the packet.
+     *
+     * Default action. Packet has nowhere to go
+     * and will be dropped.
+     */
+    SAI_BUFFER_PROFILE_PACKET_ADMISSION_FAIL_ACTION_DROP,
+
+    /**
+     * @brief Trim the packet.
+     *
+     * Try sending a shortened packet over a different
+     * queue. Original packet will be dropped and trimmed copy of the packet will be send.
+     * The IP length and checksum fields will be updated in a trimmed copy.
+     * SAI_QUEUE_STAT_DROPPED_PACKETS as well as SAI_QUEUE_STAT_DROPPED_BYTES
+     * will count the original discarded frames even if they will be trimmed afterwards.
+     * Interface statistics must show dropped packets.
+     * Interface statistics may show sent trimmed packets.
+     */
+    SAI_BUFFER_PROFILE_PACKET_ADMISSION_FAIL_ACTION_DROP_AND_TRIM,
+} sai_buffer_profile_packet_admission_fail_action_t;
+```
+```
+    /**
+     * @brief Buffer profile discard action
+     *
+     * Action to be taken upon packet discard due to
+     * buffer profile configuration. Applicable only
+     * when attached to a queue.
+     *
+     * @type sai_buffer_profile_packet_admission_fail_action_t
+     * @flags CREATE_AND_SET
+     * @default SAI_BUFFER_PROFILE_PACKET_ADMISSION_FAIL_ACTION_DROP
+     */
+    SAI_BUFFER_PROFILE_ATTR_PACKET_ADMISSION_FAIL_ACTION,
+```
+
+Trimming engine attributes are configured globally.
+```
+    /**
+     * @brief Trim packets to this size to reduce bandwidth
+     *
+     * @type sai_uint32_t
+     * @flags CREATE_AND_SET
+     * @default 128
+     */
+    SAI_SWITCH_ATTR_PACKET_TRIMMING_SIZE,
+
+    /**
+     * @brief New packet trimming DSCP value
+     *
+     * @type sai_uint8_t
+     * @flags CREATE_AND_SET
+     * @default 0
+     */
+    SAI_SWITCH_ATTR_PACKET_TRIMMING_DSCP_VALUE,
+
+    /**
+     * @brief Is the new queue index for a trimmed packet mapped from DSCP
+     *
+     * @type sai_bool_t
+     * @flags READ_ONLY
+     */
+    SAI_SWITCH_ATTR_PACKET_TRIMMING_QUEUE_INDEX_MAPPED_FROM_DSCP,
+
+    /**
+     * @brief New packet trimming queue index
+     *
+     * @type sai_uint8_t
+     * @flags CREATE_AND_SET
+     * @default 0
+     * @validonly SAI_SWITCH_ATTR_PACKET_TRIMMING_QUEUE_INDEX_MAPPED_FROM_DSCP == false
+     */
+    SAI_SWITCH_ATTR_PACKET_TRIMMING_QUEUE_INDEX,
+```
+
+If more granularity is needed (e.g. trim a specific protocol, or packets within protocol), ACL action is added to disable trimming even if the packet is eligible due to a queue with a buffer profile attached that has trimming enabled.
+```
+    /**
+     * @brief Disable packet trimming for a given match condition.
+     *
+     * This rule takes effect only when packet trimming is configured on a buffer profile of a queue to which a packet belongs.
+     *
+     * @type sai_acl_action_data_t bool
+     * @flags CREATE_AND_SET
+     * @default disabled
+     */
+    SAI_ACL_ENTRY_ATTR_ACTION_DISABLE_TRIMMING = SAI_ACL_ENTRY_ATTR_ACTION_START + 0x39,
+```
+
+Both the queue and the port have the packet counter to reflect the number of trimmed packet.
+```
+    /** Packets trimmed due to failed admission [uint64_t] */
+    SAI_QUEUE_STAT_TRIMMED_PACKETS = 0x00000028,
+```
+```
+    /** Packets trimmed due to failed shared buffer admission [uint64_t] */
+    SAI_PORT_STAT_TRIMMED_PACKETS,
+```
diff --git a/inc/saiacl.h b/inc/saiacl.h
@@ -288,6 +288,9 @@ typedef enum _sai_acl_action_type_t
 
     /** Next Chain Group */
     SAI_ACL_ACTION_TYPE_CHAIN_REDIRECT = 0x00000038,
+
+    /** Disable packet trimming */
+    SAI_ACL_ACTION_TYPE_DISABLE_TRIMMING = 0x00000039,
 } sai_acl_action_type_t;
 
 /**
@@ -3221,10 +3224,21 @@ typedef enum _sai_acl_entry_attr_t
      */
     SAI_ACL_ENTRY_ATTR_ACTION_CHAIN_REDIRECT = SAI_ACL_ENTRY_ATTR_ACTION_START + 0x38,
 
+    /**
+     * @brief Disable packet trimming for a given match condition.
+     *
+     * This rule takes effect only when packet trimming is configured on a buffer profile of a queue to which a packet belongs.
+     *
+     * @type sai_acl_action_data_t bool
+     * @flags CREATE_AND_SET
+     * @default disabled
+     */
+    SAI_ACL_ENTRY_ATTR_ACTION_DISABLE_TRIMMING = SAI_ACL_ENTRY_ATTR_ACTION_START + 0x39,
+
     /**
      * @brief End of Rule Actions
      */
-    SAI_ACL_ENTRY_ATTR_ACTION_END = SAI_ACL_ENTRY_ATTR_ACTION_CHAIN_REDIRECT,
+    SAI_ACL_ENTRY_ATTR_ACTION_END = SAI_ACL_ENTRY_ATTR_ACTION_DISABLE_TRIMMING,
 
     /**
      * @brief End of ACL Entry attributes

diff --git a/inc/saibuffer.h b/inc/saibuffer.h
@@ -590,6 +590,33 @@ typedef enum _sai_buffer_profile_threshold_mode_t
 
 } sai_buffer_profile_threshold_mode_t;
 
+/**
+ * @brief Enum defining queue actions in case the packet fails to pass the admission control.
+ */
+typedef enum _sai_buffer_profile_packet_admission_fail_action_t
+{
+    /**
+     * @brief Drop the packet.
+     *
+     * Default action. Packet has nowhere to go
+     * and will be dropped.
+     */
+    SAI_BUFFER_PROFILE_PACKET_ADMISSION_FAIL_ACTION_DROP,
+
+    /**
+     * @brief Trim the packet.
+     *
+     * Try sending a shortened packet over a different
+     * queue. Original packet will be dropped and trimmed copy of the packet will be send.
+     * The IP length and checksum fields will be updated in a trimmed copy.
+     * SAI_QUEUE_STAT_DROPPED_PACKETS as well as SAI_QUEUE_STAT_DROPPED_BYTES
+     * will count the original discarded frames even if they will be trimmed afterwards.
+     * Interface statistics must show dropped packets.
+     * Interface statistics may show sent trimmed packets.
+     */
+    SAI_BUFFER_PROFILE_PACKET_ADMISSION_FAIL_ACTION_DROP_AND_TRIM,
+} sai_buffer_profile_packet_admission_fail_action_t;
+
 /**
  * @brief Enum defining buffer profile attributes.
  */
@@ -711,6 +738,19 @@ typedef enum _sai_buffer_profile_attr_t
      */
     SAI_BUFFER_PROFILE_ATTR_XON_OFFSET_TH,
 
+    /**
+     * @brief Buffer profile discard action
+     *
+     * Action to be taken upon packet discard due to
+     * buffer profile configuration. Applicable only
+     * when attached to a queue.
+     *
+     * @type sai_buffer_profile_packet_admission_fail_action_t
+     * @flags CREATE_AND_SET
+     * @default SAI_BUFFER_PROFILE_PACKET_ADMISSION_FAIL_ACTION_DROP
+     */
+    SAI_BUFFER_PROFILE_ATTR_PACKET_ADMISSION_FAIL_ACTION,
+
     /**
      * @brief End of attributes
      */

diff --git a/inc/saiport.h b/inc/saiport.h
@@ -3304,6 +3304,9 @@ typedef enum _sai_port_stat_t
     /** Count of total bits corrected by FEC. Counter will increment monotonically. */
     SAI_PORT_STAT_IF_IN_FEC_CORRECTED_BITS,
 
+    /** Packets trimmed due to failed shared buffer admission [uint64_t] */
+    SAI_PORT_STAT_TRIMMED_PACKETS,
+
     /** Port stat in drop reasons range start */
     SAI_PORT_STAT_IN_DROP_REASON_RANGE_BASE = 0x00001000,
 

diff --git a/inc/saiqueue.h b/inc/saiqueue.h
@@ -418,6 +418,9 @@ typedef enum _sai_queue_stat_t
     /** Queue delay watermark in nanoseconds [uint64_t] */
     SAI_QUEUE_STAT_DELAY_WATERMARK_NS = 0x00000027,
 
+    /** Packets trimmed due to failed admission [uint64_t] */
+    SAI_QUEUE_STAT_TRIMMED_PACKETS = 0x00000028,
+
     /** Custom range base value */
     SAI_QUEUE_STAT_CUSTOM_RANGE_BASE = 0x10000000
 

diff --git a/inc/saiswitch.h b/inc/saiswitch.h
@@ -610,6 +610,30 @@ typedef enum _sai_switch_hostif_oper_status_update_mode_t
 
 } sai_switch_hostif_oper_status_update_mode_t;
 
+/**
+ * @brief Attribute data for SAI_SWITCH_ATTR_HOSTIF_OPER_STATUS_UPDATE_MODE.
+ */
+typedef enum _sai_packet_trimming_queue_resolution_mode_t
+{
+    /**
+     * @brief Static queue resolution.
+     *
+     * In this mode, a new queue for the trimmed packet is set directly
+     * by the application.
+     */
+    SAI_PACKET_TRIMMING_QUEUE_RESOLUTION_MODE_STATIC,
+
+    /**
+     * @brief Dynamic queue resolution.
+     *
+     * In this mode, a new queue for the trimmed packet is resolved
+     * using QOS maps, applied to a new DSCP value that was provided
+     * for a trimmed packet.
+     */
+    SAI_PACKET_TRIMMING_QUEUE_RESOLUTION_MODE_DYNAMIC,
+
+} sai_packet_trimming_queue_resolution_mode_t;
+
 /**
  * @brief Attribute Id in sai_set_switch_attribute() and
  * sai_get_switch_attribute() calls.
@@ -3070,6 +3094,43 @@ typedef enum _sai_switch_attr_t
      */
     SAI_SWITCH_ATTR_SELECTIVE_COUNTER_LIST,
 
+    /**
+     * @brief Trim packets to this size to reduce bandwidth
+     *
+     * @type sai_uint32_t
+     * @flags CREATE_AND_SET
+     * @default 128
+     */
+    SAI_SWITCH_ATTR_PACKET_TRIMMING_SIZE,
+
+    /**
+     * @brief New packet trimming DSCP value
+     *
+     * @type sai_uint8_t
+     * @flags CREATE_AND_SET
+     * @default 0
+     */
+    SAI_SWITCH_ATTR_PACKET_TRIMMING_DSCP_VALUE,
+
+    /**
+     * @brief Queue mapping mode for a trimmed packet
+     *
+     * @type sai_packet_trimming_queue_resolution_mode_t
+     * @flags CREATE_AND_SET
+     * @default SAI_PACKET_TRIMMING_QUEUE_RESOLUTION_MODE_STATIC
+     */
+    SAI_SWITCH_ATTR_PACKET_TRIMMING_QUEUE_RESOLUTION_MODE,
+
+    /**
+     * @brief New packet trimming queue index
+     *
+     * @type sai_uint8_t
+     * @flags CREATE_AND_SET
+     * @default 0
+     * @validonly SAI_SWITCH_ATTR_PACKET_TRIMMING_QUEUE_RESOLUTION_MODE == SAI_PACKET_TRIMMING_QUEUE_RESOLUTION_MODE_STATIC
+     */
+    SAI_SWITCH_ATTR_PACKET_TRIMMING_QUEUE_INDEX,
+
     /**
      * @brief End of attributes
      */