[xorblurb]

Needing to wake up usermode is not necessarily an insurmountable obstacle; under Linux you can use a PREEMPT config. Storming a network card having unwanted consequences can also be mitigated: under Linux you have some network device driver that use an hybrid interrupt/polling approach with the NAPI. Combining both should theoretically allow a system to generate sound smoothly in the described conditions.

[amluto]

IMO you shouldn't really need to wake user mode that often. Just let user code buffer the output samples well ahead of the hardware needing them and have the kernel do the copies when needed.

[xorblurb]

Of course if you can do that, it's really good. However, sometimes you need low latency.