How seastar invoke codes on different cpus?

I am currently working with seastart framework, and find it claims that seastart can submit task to different cpus.

Seastar claims that it shares nothing between different coers.

So I think seastar binds differnet threads to different cpus, and make different tasks submited to different background threads(called engine、container or something).

How seastar achieve this, use pthread_setaffinity_np ?

But before task submitted, codes still work on random thread? Just key resources like network socket or storages are distributed to different cpus by coding using smp::submit_to explicitly?