[SlimDX] Compute Shader question

I am working on a compute shader and I want to do some speed test... I read somewhere that compute shaders are being executed asynchronously and I wonder if that is the case with the following call:

device.ImmediateContext.Dispatch(1, height, 1);

Can I just time how long this call takes or do I need to do queries or mapping of the result set to get accurate measurements?

Thanks
Marcel