Add XDP-level counters for improved visibility

Summary:
Add dedicated XDP-level statistics counters to improve observability of packet processing at the XDP layer.
introduces new counters: `XDP_TOTAL_CNTR`, `XDP_TX_CNTR`, `XDP_DROP_CNTR`, and `XDP_PASS_CNTR`

Reviewed By: nikhildl12

Differential Revision: D82544156

fbshipit-source-id: 7045912a5ec4bd9fda1e30b7cf8ca0f6b1d60eaa

Author: p-shah256

katran/lib/bpf/balancer.bpf.c

@@ -1077,22 +1077,50 @@ int balancer_ingress(struct xdp_md* ctx) {
   __u32 eth_proto;
   __u32 nh_off;
   nh_off = sizeof(struct ethhdr);
+  __u64 data_len = data_end - data;
+  struct lb_stats* data_stats;
+  __u32 stats_key;
 
   if (data + nh_off > data_end) {
     // bogus packet, len less than minimum ethernet frame size
     return XDP_DROP;
   }
 
+  stats_key = MAX_VIPS + XDP_TOTAL_CNTR;
+  data_stats = bpf_map_lookup_elem(&stats, &stats_key);
+  if (!data_stats) {
+    return XDP_DROP;
+  }
+  data_stats->v1 += 1;
+  data_stats->v2 += data_len;
+
   eth_proto = eth->h_proto;
 
+  int action;
   if (eth_proto == BE_ETH_P_IP) {
-    return process_packet(ctx, nh_off, false);
+    action = process_packet(ctx, nh_off, false);
   } else if (eth_proto == BE_ETH_P_IPV6) {
-    return process_packet(ctx, nh_off, true);
+    action = process_packet(ctx, nh_off, true);
   } else {
     // pass to tcp/ip stack
-    return XDP_PASS;
+    action = XDP_PASS;
   }
+
+  if (action == XDP_PASS) {
+    stats_key = MAX_VIPS + XDP_PASS_CNTR;
+  } else if (action == XDP_DROP) {
+    stats_key = MAX_VIPS + XDP_DROP_CNTR;
+  } else if (action == XDP_TX) {
+    stats_key = MAX_VIPS + XDP_TX_CNTR;
+  }
+
+  data_stats = bpf_map_lookup_elem(&stats, &stats_key);
+  if (!data_stats) {
+    return XDP_DROP;
+  }
+  data_stats->v1 += 1;
+  data_stats->v2 += data_len;
+  return action;
 }
 
 char _license[] SEC("license") = "GPL";

katran/lib/bpf/balancer_consts.h

@@ -254,7 +254,11 @@
 #define NO_FLAGS 0
 
 // offset of the lru cache hit related counters
+/* v1 tracks total vip packets (no longer used for lru calculations)
+v2 tracks lru misses */
 #define LRU_CNTRS 0
+/* v1 tracks misses for TCP syns
+v2 tracks misses for TCP non syns */
 #define LRU_MISS_CNTR 1
 #define NEW_CONN_RATE_CNTR 2
 #define FALLBACK_LRU_CNTR 3
@@ -281,6 +285,10 @@
 #define XPOP_DECAP_SUCCESSFUL 14
 // Tracks packets dst invalidated due to UDP flow migration
 #define UDP_FLOW_MIGRATION_STATS 15
+#define XDP_TOTAL_CNTR 16 // total packets "touched" by katran
+#define XDP_TX_CNTR 17 // total packets sent to backend
+#define XDP_DROP_CNTR 18 // total packets dropped by katran
+#define XDP_PASS_CNTR 19 // packets passed up to the kernel
 
 // indice for all stats maps defined above correspond to entries in the map
 // stats starting from the index MAX_VIPS. The max_entries of stats is