I suspect that you’re misreading this identifier. You should read it as “dispatch queue wakeup with QoS, taking the slow path”. Many algorithms within Dispatch have a fast path, which is the typical case when things go well (no lock contention and so on). Clearly the existence of a fast path implies that there also exists a slow path, and that’s what this routine implements.
If you want to see this in context you can look at the Dispatch source code for this routine.
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