[IoContext] wrap CQ locking in if constexpr

We don't need to pay the overhead of the atomic operations on each dispatch loop if there is no concurrent access to worker CQs.

emper/io/IoContext.cpp

@@ -211,24 +211,26 @@ reap_cqes:
 	LOGD("Reaping completions for worker " << std::to_string(worker->getWorkerId()));
 	std::array<struct io_uring_cqe *, CQE_BATCH_COUNT> cqes;
 
-	// Someone else is currently reaping completions
-	if constexpr (callerEnvironment == CallerEnvironment::EMPER) {
-		if (unlikely(!cq_lock.try_lock())) {
-			LOGD("worker unsuccessful try_lock");
-			return 0;
-		}
-	} else {
-		// We can not reap completions of this IoContext to not race
-		// with the sleeping worker.
-		if (waitInflight.load(std::memory_order_acquire)) {
-			LOGD("Not reaping worker " << std::to_string(worker->getWorkerId())
-																 << " since this worker is already waiting for its CQEs");
-			return 0;
-		}
+	if constexpr (needsCqLock) {
+		// Someone else is currently reaping completions
+		if constexpr (callerEnvironment == CallerEnvironment::EMPER) {
+			if (unlikely(!cq_lock.try_lock())) {
+				LOGD("worker unsuccessful try_lock");
+				return 0;
+			}
+		} else {
+			// We can not reap completions of this IoContext to not race
+			// with the sleeping worker.
+			if (waitInflight.load(std::memory_order_acquire)) {
+				LOGD("Not reaping worker " << std::to_string(worker->getWorkerId())
+																	 << " since this worker is already waiting for its CQEs");
+				return 0;
+			}
 
-		if (!cq_lock.try_lock_or_increment()) {
-			LOGD("Global completer unsuccessful try_lock_or_increment");
-			return 0;
+			if (!cq_lock.try_lock_or_increment()) {
+				LOGD("Global completer unsuccessful try_lock_or_increment");
+				return 0;
+			}
 		}
 	}
 
@@ -245,7 +247,10 @@ reap_cqes:
 
 	io_uring_cq_advance(&ring, count);
 
-	uint32_t globalCompleterAttempts = cq_lock.unlock();
+	uint32_t globalCompleterAttempts;
+	if constexpr (needsCqLock) {
+		globalCompleterAttempts = cq_lock.unlock();
+	}
 
 	LOGD("got " << count << " cqes from worker " << worker->getWorkerId() << "'s io_uring");
 
@@ -336,7 +341,7 @@ reap_cqes:
 	}
 
 	// check if lost wakeup was possible
-	if constexpr (callerEnvironment == CallerEnvironment::EMPER) {
+	if constexpr (needsCqLock && callerEnvironment == CallerEnvironment::EMPER) {
 		bool reReap = false;
 		// TODO: How sure are we that this is unlikely?
 		if (unlikely(globalCompleterAttempts > maxRaceFreeCompleterAttempts)) {