* The IOScheduler does not create as many operations as it can before

executing them. Doesn't really make any difference ATM.
* Handle B_BUSY returned by DMAResource::TranslateNext() correctly.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27186 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/device_manager/IOScheduler.cpp

@@ -272,13 +272,13 @@ IOScheduler::_GetOperation(bool wait)
 
 
 IORequest*
-IOScheduler::_GetNextUnscheduledRequest()
+IOScheduler::_GetNextUnscheduledRequest(bool wait)
 {
 	while (true) {
 		MutexLocker locker(fLock);
 		IORequest* request = fUnscheduledRequests.RemoveHead();
 
-		if (request != NULL)
+		if (request != NULL || !wait)
 			return request;
 
 		// Wait for new requests. First check whether any finisher work has
@@ -306,33 +306,72 @@ IOScheduler::_GetNextUnscheduledRequest()
 }
 
 
+bool
+IOScheduler::_PrepareRequestOperations(IORequest* request,
+	IOOperationList& operations, int32& operationsPrepared)
+{
+	if (fDMAResource != NULL) {
+		while (request->RemainingBytes() > 0) {
+			IOOperation* operation = _GetOperation(operations.IsEmpty());
+			if (operation == NULL)
+				return false;
+
+			status_t status = fDMAResource->TranslateNext(request,
+				operation);
+			if (status != B_OK) {
+				operation->SetParent(NULL);
+				MutexLocker locker(fLock);
+				fUnusedOperations.Add(operation);
+
+				// B_BUSY means some resource (DMABuffers or
+				// DMABounceBuffers) was temporarily unavailable. That's OK,
+				// we'll retry later.
+				if (status == B_BUSY)
+					return false;
+
+				AbortRequest(request, status);
+				return true;
+			}
+
+			operations.Add(operation);
+			operationsPrepared++;
+		}
+	} else {
+// TODO: If the device has block size restrictions, we might need to use a
+// bounce buffer.
+		IOOperation* operation = _GetOperation(true);
+// TODO: Prepare() can fail!
+		operation->Prepare(request);
+		operation->SetOriginalRange(request->Offset(), request->Length());
+		request->Advance(request->Length());
+		operationsPrepared++;
+	}
+
+	return true;
+}
+
+
 status_t
 IOScheduler::_Scheduler()
 {
 // TODO: This is a no-op scheduler. Implement something useful!
 	while (true) {
-		IORequest* request = _GetNextUnscheduledRequest();
+		IOOperationList operations;
+		int32 operationCount = 0;
 
+		while (IORequest* request
+				= _GetNextUnscheduledRequest(operationCount == 0)) {
 			TRACE("IOScheduler::_Scheduler(): request: %p\n", request);
 
-		if (fDMAResource != NULL) {
-			IOOperationList operations;
-			while (request->RemainingBytes() > 0) {
-				IOOperation* operation = _GetOperation(operations.IsEmpty());
-				if (operation == NULL)
-					break;
-
-				status_t status = fDMAResource->TranslateNext(request,
-					operation);
-				if (status != B_OK) {
-// TODO: Handle correctly! E.g. B_BUSY just means that some resource (e.g.
-// DMA buffers) isn't available ATM. We should execute the operations we have
-// so far and wait for resources to become available again.
-					AbortRequest(request, status);
-					break;
+			int32 requestOperations = 0;
+			if (!_PrepareRequestOperations(request, operations,
+					requestOperations) && requestOperations == 0) {
+				// no operation prepared at all -- re-add the request for the
+				// next round
+				MutexLocker locker(fLock);
+				fUnscheduledRequests.Add(request, false);
 			}
-
-				operations.Add(operation);
+			operationCount += requestOperations;
 		}
 
 		while (IOOperation* operation = operations.RemoveHead()) {
@@ -341,15 +380,6 @@ IOScheduler::_Scheduler()
 
 			fIOCallback(fIOCallbackData, operation);
 		}
-		} else {
-// TODO: If the device has block size restrictions, we might need to use a
-// bounce buffer.
-			IOOperation* operation = _GetOperation(true);
-			operation->Prepare(request);
-			operation->SetOriginalRange(request->Offset(), request->Length());
-			request->Advance(request->Length());
-			fIOCallback(fIOCallbackData, operation);
-		}
 	}
 
 	return B_OK;

src/system/kernel/device_manager/IOScheduler.h

@@ -48,7 +48,10 @@ private:
 			void				_Finisher();
 			bool				_FinisherWorkPending();
 			IOOperation*		_GetOperation(bool wait);
-			IORequest*			_GetNextUnscheduledRequest();
+			IORequest*			_GetNextUnscheduledRequest(bool wait);
+			bool				_PrepareRequestOperations(IORequest* request,
+									IOOperationList& operations,
+									int32& operationsPrepared);
 			status_t			_Scheduler();
 	static	status_t			_SchedulerThread(void* self);
 			status_t			_RequestNotifier();