chenBright commented on code in PR #3009:
URL: https://github.com/apache/brpc/pull/3009#discussion_r2173632622


##########
src/bthread/task_control.cpp:
##########
@@ -524,12 +525,29 @@ void TaskControl::print_rq_sizes(std::ostream& os) {
 
 double TaskControl::get_cumulated_worker_time() {
     int64_t cputime_ns = 0;
+    int64_t now = butil::cpuwide_time_ns();
     BAIDU_SCOPED_LOCK(_modify_group_mutex);
     for_each_task_group([&](TaskGroup* g) {
         if (g) {
-            cputime_ns += g->_cumulated_cputime_ns;
+            // With the acquire-release atomic operation, the CPU time of the 
bthread is
+            // only calculated once through `_cumulated_cputime_ns' or 
`_last_run_ns'.
+            cputime_ns += 
g->_cumulated_cputime_ns.load(butil::memory_order_acquire);
+            // The bthread is still running on the worker,
+            // so we need to add the elapsed time since it started.
+            // In extreme cases, before getting `_last_run_ns_in_tc',
+            // `_last_run_ns_in_tc' may have been updated multiple times,
+            // and `cputime_ns' will miss some cpu time, which is ok.
+            int64_t last_run_ns = g->_last_run_ns;
+            if (last_run_ns > _last_get_cumulated_time_ns) {
+                g->_last_run_ns_in_tc = last_run_ns;
+                cputime_ns += now - last_run_ns;
+            } else if (last_run_ns == g->_last_run_ns_in_tc) {
+                // The bthread is still running on the same worker.
+                cputime_ns += now - last_run_ns;
+            }

Review Comment:
   Perhaps we can use the implicit feature of modern CPUs that 128-bit aligned 
load/store operations are atomic to implement atomic operations on combination 
of `_cumulated_cputime_ns` and `_last_run_ns`.
   
   x86_64: `_mm_load_si128`, `_mm_store_si128`
   Arm and later: `vld1q_s64`
   
   For scenarios that do not support 128-bit atomic operations, use the current 
PR implementation without lock. For a monitoring item used for debugging, this 
trade-off is reasonable.



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