why no semaphores? events are a bit fine grained

While level 0 has fences and events it doesn't appear to have any semaphore support.

Events can be a messy solution from a scheduler point of view, as they pretty much block the GPU command processing hard at a point in time, some GPUs can reschedule other command streams, some can't. So while useful events can be a bit of a large hammer to hit a system with from a user application. Also GPU selected events invariably mean the CPU side is spinning on some memory location polling the event, again not really a great thing to have to depend on.

Vulkan recently added timeline semaphores and perhaps there should be some consideration of adding them to Level 0 as a better scheduling mechanism.

Start by reviewing the Level Zero specification headers and loader, focusing on the existing level 0 fences and events APIs. Compare their scheduling behavior with Vulkan timeline semaphores as described in the issue. Done would require a decided semaphore design and corresponding specification changes, but the issue does not define the API or acceptance criteria.