limit minimum value of max concurrency when all requests failed

src/brpc/policy/auto_concurrency_limiter.cpp

@@ -189,7 +189,7 @@ bool AutoConcurrencyLimiter::AddSample(int error_code,
         UpdateMaxConcurrency(sampling_time_us);
     } else {
         // All request failed
-        _max_concurrency /= 2;
+        AdjustMaxConcurrency(_max_concurrency / 2);
     }
     ResetSampleWindow(sampling_time_us);
     return true;
@@ -222,6 +222,13 @@ void AutoConcurrencyLimiter::UpdateQps(double qps) {
     }
 }
 
+void AutoConcurrencyLimiter::AdjustMaxConcurrency(int next_max_concurrency) {
+    next_max_concurrency = std::max(bthread::FLAGS_bthread_concurrency, next_max_concurrency);
+    if (next_max_concurrency != _max_concurrency) {
+        _max_concurrency = next_max_concurrency;
+    }
+}
+
 void AutoConcurrencyLimiter::UpdateMaxConcurrency(int64_t sampling_time_us) {
     int32_t total_succ_req = _total_succ_req.load(butil::memory_order_relaxed);
     double failed_punish = _sw.total_failed_us * FLAGS_auto_cl_fail_punish_ratio;
@@ -253,10 +260,7 @@ void AutoConcurrencyLimiter::UpdateMaxConcurrency(int64_t sampling_time_us) {
             _min_latency_us * _ema_max_qps / 1000000 *  (1 + _explore_ratio);
     }
 
-    next_max_concurrency = std::max(bthread::FLAGS_bthread_concurrency, next_max_concurrency);
-    if (next_max_concurrency != _max_concurrency) {
-        _max_concurrency = next_max_concurrency;
-    }
+    AdjustMaxConcurrency(next_max_concurrency);
 }
 
 }  // namespace policy

src/brpc/policy/auto_concurrency_limiter.h

@@ -62,6 +62,8 @@ private:
     void UpdateMinLatency(int64_t latency_us);
     void UpdateQps(double qps);
 
+    void AdjustMaxConcurrency(int next_max_concurrency);
+
     // modified per sample-window or more
     int _max_concurrency;
     int64_t _remeasure_start_us;