server: refactor sleep handling, allow access /metrics during sleep (#27376)

* add cached responses

* refactor on_sleeping_state

* allow accessing metrics during sleep

* metrics task should not reset timer

* updated docs

* fix

* fix get_res_model_info

* add test

* fix a race condition

* split metrics and slots tasks / results

* should_reset_buckets

tools/server/server-queue.cpp

@@ -3,6 +3,7 @@
 
 #include "log.h"
 
+#include <algorithm>
 #include <chrono>
 #include <thread>
 
@@ -20,6 +21,10 @@
 // server_queue
 //
 
+static bool task_resets_idle_timer(server_task_type type) {
+    return type != SERVER_TASK_TYPE_METRICS;
+}
+
 int server_queue::post(server_task && task, bool front) {
     std::unique_lock<std::mutex> lock(mutex_tasks);
     GGML_ASSERT(task.id != -1);
@@ -27,20 +32,24 @@ int server_queue::post(server_task && task, bool front) {
     if (task.type == SERVER_TASK_TYPE_CANCEL) {
         cleanup_pending_task(task.id_target);
     }
-    const int task_id = task.id;
+    const int  task_id     = task.id;
+    const bool reset_timer = task_resets_idle_timer(task.type);
     QUE_DBG("new task, id = %d, front = %d\n", task_id, front);
     if (front) {
         queue_tasks.push_front(std::move(task));
     } else {
         queue_tasks.push_back(std::move(task));
     }
-    time_last_task = ggml_time_ms();
+    if (reset_timer) {
+        time_last_task = ggml_time_ms();
+    }
     condition_tasks.notify_one();
     return task_id;
 }
 
 int server_queue::post(std::vector<server_task> && tasks, bool front) {
     std::unique_lock<std::mutex> lock(mutex_tasks);
+    bool reset_timer = false;
     for (auto & task : tasks) {
         if (task.id == -1) {
             task.id = id++;
@@ -49,6 +58,7 @@ int server_queue::post(std::vector<server_task> && tasks, bool front) {
         if (task.type == SERVER_TASK_TYPE_CANCEL) {
             cleanup_pending_task(task.id_target);
         }
+        reset_timer |= task_resets_idle_timer(task.type);
         QUE_DBG("new task, id = %d/%d, front = %d\n", task.id, (int) tasks.size(), front);
         if (front) {
             queue_tasks.push_front(std::move(task));
@@ -56,7 +66,9 @@ int server_queue::post(std::vector<server_task> && tasks, bool front) {
             queue_tasks.push_back(std::move(task));
         }
     }
-    time_last_task = ggml_time_ms();
+    if (reset_timer) {
+        time_last_task = ggml_time_ms();
+    }
     condition_tasks.notify_one();
     return 0;
 }
@@ -294,11 +306,14 @@ void server_queue::start_loop(int64_t idle_sleep_ms) {
         QUE_DBG("%s", "update slots\n");
 
         // this will run the main inference process for all slots
+        const int64_t t_update_slots = ggml_time_ms();
         callback_update_slots();
         {
             // update_slots() may take a while to finish, we need to make sure it's not counted as idle
+            // shift instead of reset, so that non-task_resets_idle_timer tasks do not delay the sleep
             std::unique_lock<std::mutex> lock(mutex_tasks);
-            time_last_task = ggml_time_ms();
+            const int64_t now = ggml_time_ms();
+            time_last_task = std::min(now, time_last_task + (now - t_update_slots));
         }
 
         QUE_DBG("%s", "waiting for new tasks\n");
@@ -312,7 +327,10 @@ void server_queue::start_loop(int64_t idle_sleep_ms) {
             if (should_sleep()) {
                 QUE_INF("%s", "entering sleeping state\n");
                 sleeping = true;
-                callback_sleeping_state(true);
+                // Call order cb0 -> cb1 -> cb{N}
+                for (auto & cb : callback_sleeping_state) {
+                    cb(true);
+                }
                 req_stop_sleeping = false;
                 // wait until we are requested to exit sleeping state
                 condition_tasks.wait(lock, [&]{
@@ -323,7 +341,10 @@ void server_queue::start_loop(int64_t idle_sleep_ms) {
                 }
                 QUE_INF("%s", "exiting sleeping state\n");
                 req_stop_sleeping = false;
-                callback_sleeping_state(false);
+                // Call order cb{N} -> cb1 -> cb0
+                for (size_t i = callback_sleeping_state.size(); i > 0; i--) {
+                    callback_sleeping_state[i - 1](false);
+                }
                 sleeping = false;
                 time_last_task = ggml_time_ms();
                 condition_tasks.notify_all(); // notify wait_until_no_sleep()