Pinned Memory NVIDIA

This presentation says that using the Map/Unmap APIs should use pinned memory:

So I have code like this to upload data to GPU:

auto ptr = cmdQueue.enqueueMapBuffer(_gpuBuffer, CL_TRUE,

	memcpy(ptr,, numBytes);

	ThrowIfFailed(cmdQueue.enqueueUnmapMemObject(_gpuBuffer, ptr, waitEvents, cmdEvent));

So I am concerned about having to block on the enqueueMapBuffer? Does this cause a sync point where it waits for all commands to finish up to this point? Or will is still return pretty fast (when the mapped pointer can be returned)?