DirectX 11 wasn’t well suited for asynchronous shading. The same heavily abstracted, driver & OS controlled rendering path that gave DX11 its relatively high CPU overhead and poor multi-core command buffer submission also enforced very
stringent processing requirements.
DX11 was a serial API through and through, both for command buffer execution and as it turned out shader execution.
Along with making it much easier to
submit work from multiple threads over multiple cores, all of these APIs are also making significant changes in how work is executed.
With the ability to accept work from multiple threads, work can now be more readily executed in parallel and asynchronously.
(Quelle)