feat: Add output token counter to frontend metrics (#4202)

Signed-off-by: Aryan Bagade <aryan@aryanbagade.com>

lib/bindings/python/src/dynamo/prometheus_names.py

@@ -55,6 +55,8 @@ class frontend_service:
     INPUT_SEQUENCE_TOKENS = "input_sequence_tokens"
     # Output sequence length in tokens
     OUTPUT_SEQUENCE_TOKENS = "output_sequence_tokens"
+    # Total number of output tokens generated (counter that updates in real-time)
+    OUTPUT_TOKENS_TOTAL = "output_tokens_total"
     # Time to first token in seconds
     TIME_TO_FIRST_TOKEN_SECONDS = "time_to_first_token_seconds"
     # Inter-token latency in seconds
@@ -76,13 +78,21 @@ class frontend_service:
     MODEL_MIGRATION_LIMIT = "model_migration_limit"
 
 
-class kvbm_connector:
-    """KVBM connector"""
-
-    # KVBM connector leader
-    KVBM_CONNECTOR_LEADER = "kvbm_connector_leader"
-    # KVBM connector worker
-    KVBM_CONNECTOR_WORKER = "kvbm_connector_worker"
+class kvbm:
+    """KVBM"""
+
+    # The number of offload blocks from device to host
+    OFFLOAD_BLOCKS_D2H = "offload_blocks_d2h"
+    # The number of offload blocks from host to disk
+    OFFLOAD_BLOCKS_H2D = "offload_blocks_h2d"
+    # The number of offload blocks from device to disk (bypassing host memory)
+    OFFLOAD_BLOCKS_D2D = "offload_blocks_d2d"
+    # The number of onboard blocks from host to device
+    ONBOARD_BLOCKS_H2D = "onboard_blocks_h2d"
+    # The number of onboard blocks from disk to device
+    ONBOARD_BLOCKS_D2D = "onboard_blocks_d2d"
+    # The number of matched tokens
+    MATCHED_TOKENS = "matched_tokens"
 
 
 class kvrouter:

lib/llm/src/http/service/metrics.rs

@@ -161,6 +161,7 @@ pub struct Metrics {
     request_duration: HistogramVec,
     input_sequence_length: HistogramVec,
     output_sequence_length: HistogramVec,
+    output_tokens_counter: IntCounterVec,
     time_to_first_token: HistogramVec,
     inter_token_latency: HistogramVec,
 
@@ -266,6 +267,7 @@ impl Metrics {
     /// - `{prefix}_request_duration_seconds` - HistogramVec for the duration of requests
     /// - `{prefix}_input_sequence_tokens` - HistogramVec for input sequence length in tokens
     /// - `{prefix}_output_sequence_tokens` - HistogramVec for output sequence length in tokens
+    /// - `{prefix}_output_tokens_total` - IntCounterVec for total output tokens generated (real-time updates)
     /// - `{prefix}_time_to_first_token_seconds` - HistogramVec for time to first token in seconds
     /// - `{prefix}_inter_token_latency_seconds` - HistogramVec for inter-token latency in seconds
     ///
@@ -392,6 +394,15 @@ impl Metrics {
         )
         .unwrap();
 
+        let output_tokens_counter = IntCounterVec::new(
+            Opts::new(
+                frontend_metric_name(frontend_service::OUTPUT_TOKENS_TOTAL),
+                "Total number of output tokens generated (updates in real-time)",
+            ),
+            &["model"],
+        )
+        .unwrap();
+
         // Time to first token buckets: configurable via DYN_METRICS_TTFT_{MIN,MAX,COUNT}
         let (ttft_min, ttft_max, ttft_count) =
             parse_bucket_config("DYN_METRICS_TTFT", 0.001, 480.0, 18);
@@ -487,6 +498,7 @@ impl Metrics {
             request_duration,
             input_sequence_length,
             output_sequence_length,
+            output_tokens_counter,
             time_to_first_token,
             inter_token_latency,
             model_total_kv_blocks,
@@ -581,6 +593,7 @@ impl Metrics {
         registry.register(Box::new(self.request_duration.clone()))?;
         registry.register(Box::new(self.input_sequence_length.clone()))?;
         registry.register(Box::new(self.output_sequence_length.clone()))?;
+        registry.register(Box::new(self.output_tokens_counter.clone()))?;
         registry.register(Box::new(self.time_to_first_token.clone()))?;
         registry.register(Box::new(self.inter_token_latency.clone()))?;
 
@@ -832,6 +845,12 @@ impl ResponseMetricCollector {
             return;
         }
 
+        // Increment the real-time output tokens counter
+        self.metrics
+            .output_tokens_counter
+            .with_label_values(&[&self.model])
+            .inc_by(num_tokens as u64);
+
         if self.is_first_token {
             // NOTE: when there are multiple tokens in the first response,
             // we use the full response time as TTFT and ignore the ITL
@@ -1187,4 +1206,151 @@ mod tests {
             );
         }
     }
+
+    #[test]
+    fn test_output_tokens_counter_increments() {
+        let metrics = Arc::new(Metrics::new());
+        let registry = prometheus::Registry::new();
+        metrics.register(&registry).unwrap();
+
+        let model = "test-model";
+
+        // Create response collector
+        let mut collector = metrics.clone().create_response_collector(model);
+
+        // Simulate first chunk (5 tokens)
+        collector.observe_response(100, 5);
+
+        // Verify counter incremented by 5
+        let counter_value = metrics
+            .output_tokens_counter
+            .with_label_values(&[model])
+            .get();
+        assert_eq!(counter_value, 5);
+
+        // Simulate second chunk (10 tokens)
+        collector.observe_response(100, 10);
+
+        // Verify counter incremented to 15
+        let counter_value = metrics
+            .output_tokens_counter
+            .with_label_values(&[model])
+            .get();
+        assert_eq!(counter_value, 15);
+
+        // Simulate third chunk (7 tokens)
+        collector.observe_response(100, 7);
+
+        // Verify counter incremented to 22
+        let counter_value = metrics
+            .output_tokens_counter
+            .with_label_values(&[model])
+            .get();
+        assert_eq!(counter_value, 22);
+    }
+
+    #[test]
+    fn test_output_tokens_counter_zero_tokens() {
+        let metrics = Arc::new(Metrics::new());
+        let registry = prometheus::Registry::new();
+        metrics.register(&registry).unwrap();
+
+        let model = "test-model";
+        let mut collector = metrics.clone().create_response_collector(model);
+
+        // Simulate chunk with zero tokens (should not increment)
+        collector.observe_response(100, 0);
+
+        // Verify counter remains 0
+        let counter_value = metrics
+            .output_tokens_counter
+            .with_label_values(&[model])
+            .get();
+        assert_eq!(counter_value, 0);
+
+        // Add some tokens
+        collector.observe_response(100, 5);
+        assert_eq!(
+            metrics
+                .output_tokens_counter
+                .with_label_values(&[model])
+                .get(),
+            5
+        );
+
+        // Try zero tokens again (should not change counter)
+        collector.observe_response(100, 0);
+        assert_eq!(
+            metrics
+                .output_tokens_counter
+                .with_label_values(&[model])
+                .get(),
+            5
+        );
+    }
+
+    #[test]
+    fn test_output_tokens_counter_multiple_models() {
+        let metrics = Arc::new(Metrics::new());
+        let registry = prometheus::Registry::new();
+        metrics.register(&registry).unwrap();
+
+        let model1 = "model-1";
+        let model2 = "model-2";
+
+        // Create collectors for different models
+        let mut collector1 = metrics.clone().create_response_collector(model1);
+        let mut collector2 = metrics.clone().create_response_collector(model2);
+
+        // Increment model1
+        collector1.observe_response(100, 10);
+        assert_eq!(
+            metrics
+                .output_tokens_counter
+                .with_label_values(&[model1])
+                .get(),
+            10
+        );
+        assert_eq!(
+            metrics
+                .output_tokens_counter
+                .with_label_values(&[model2])
+                .get(),
+            0
+        );
+
+        // Increment model2
+        collector2.observe_response(200, 20);
+        assert_eq!(
+            metrics
+                .output_tokens_counter
+                .with_label_values(&[model1])
+                .get(),
+            10
+        );
+        assert_eq!(
+            metrics
+                .output_tokens_counter
+                .with_label_values(&[model2])
+                .get(),
+            20
+        );
+
+        // Increment model1 again
+        collector1.observe_response(100, 5);
+        assert_eq!(
+            metrics
+                .output_tokens_counter
+                .with_label_values(&[model1])
+                .get(),
+            15
+        );
+        assert_eq!(
+            metrics
+                .output_tokens_counter
+                .with_label_values(&[model2])
+                .get(),
+            20
+        );
+    }
 }

lib/runtime/src/metrics/prometheus_names.rs

@@ -113,6 +113,9 @@ pub mod frontend_service {
     /// Output sequence length in tokens
     pub const OUTPUT_SEQUENCE_TOKENS: &str = "output_sequence_tokens";
 
+    /// Total number of output tokens generated (counter that updates in real-time)
+    pub const OUTPUT_TOKENS_TOTAL: &str = "output_tokens_total";
+
     /// Time to first token in seconds
     pub const TIME_TO_FIRST_TOKEN_SECONDS: &str = "time_to_first_token_seconds";