docs: fix metrics endpoint description in server README (ggml-org#22879)

* docs: fix metrics endpoint description in server README

Required model query parameter for router mode described.

Removed metrics:
- llamacpp:kv_cache_usage_ratio
- llamacpp:kv_cache_tokens

Added metrics:
- llamacpp:prompt_seconds_total
- llamacpp:tokens_predicted_seconds_total
- llamacpp:n_decode_total
- llamacpp:n_busy_slots_per_decode

* server: fix metrics type for n_busy_slots_per_decode metric

Author: willjoha

tools/server/README.md

@@ -1043,16 +1043,23 @@ If query param `?fail_on_no_slot=1` is set, this endpoint will respond with stat
 
 This endpoint is only accessible if `--metrics` is set.
 
-Available metrics:
-- `llamacpp:prompt_tokens_total`: Number of prompt tokens processed.
-- `llamacpp:tokens_predicted_total`: Number of generation tokens processed.
-- `llamacpp:prompt_tokens_seconds`: Average prompt throughput in tokens/s.
-- `llamacpp:predicted_tokens_seconds`: Average generation throughput in tokens/s.
-- `llamacpp:kv_cache_usage_ratio`: KV-cache usage. `1` means 100 percent usage.
-- `llamacpp:kv_cache_tokens`: KV-cache tokens.
-- `llamacpp:requests_processing`: Number of requests processing.
-- `llamacpp:requests_deferred`: Number of requests deferred.
-- `llamacpp:n_tokens_max`: High watermark of the context size observed.
+In *router mode* the query param `?model={model_id}` has to be set. This endpoint will respond with status code 400 `model name is missing from the request` if not set.
+
+#### Available metrics
+
+| Metric | Type | Description |
+| ------ | ---------------------- | ----------- |
+| `llamacpp:prompt_tokens_total` | Counter | Number of prompt tokens processed. |
+| `llamacpp:prompt_seconds_total` | Counter | Prompt process time in seconds. |
+| `llamacpp:prompt_tokens_seconds` | Gauge | Average prompt throughput in tokens/s. |
+| `llamacpp:tokens_predicted_total` | Counter | Number of generation tokens processed. |
+| `llamacpp:tokens_predicted_seconds_total` | Counter | Predict process time in seconds. |
+| `llamacpp:predicted_tokens_seconds` | Gauge | Average generation throughput in tokens/s. |
+| `llamacpp:requests_processing` | Gauge | Number of requests processing. |
+| `llamacpp:requests_deferred` | Gauge | Number of requests deferred. |
+| `llamacpp:n_tokens_max` | Counter | High watermark of the context size observed. |
+| `llamacpp:n_decode_total` | Counter | Total Number of llama_decode() calls. |
+| `llamacpp:n_busy_slots_per_decode` | Gauge | Average number of busy slots per llama_decode() call. |
 
 ### POST `/slots/{id_slot}?action=save`: Save the prompt cache of the specified slot to a file.
 

tools/server/server-context.cpp

@@ -3622,10 +3622,6 @@ void server_routes::init_routes() {
                     {"name",  "n_tokens_max"},
                     {"help",  "Largest observed n_tokens."},
                     {"value",  res_task->n_tokens_max}
-            }, {
-                    {"name",  "n_busy_slots_per_decode"},
-                    {"help",  "Average number of busy slots per llama_decode() call"},
-                    {"value",  (float) res_task->n_busy_slots_total / std::max((float) res_task->n_decode_total, 1.f)}
             }}},
             {"gauge", {{
                     {"name",  "prompt_tokens_seconds"},
@@ -3643,6 +3639,10 @@ void server_routes::init_routes() {
                     {"name",  "requests_deferred"},
                     {"help",  "Number of requests deferred."},
                     {"value",  (uint64_t) res_task->n_tasks_deferred}
+            },{
+                    {"name",  "n_busy_slots_per_decode"},
+                    {"help",  "Average number of busy slots per llama_decode() call"},
+                    {"value",  (float) res_task->n_busy_slots_total / std::max((float) res_task->n_decode_total, 1.f)}
             }}}
         };