A suspend point inserts GPU commands that drain the graphics pipe. The call
that inserts it does not wait for those commands, and the hardware allows one
suspend point to be in flight, but the queue implemented it by blocking the
calling thread until every accepted submission had been processed.
The frame boundary is now a queued submission of its own, ordered behind the
graphics work it ends, and processing it flushes what the frame recorded. The
caller returns immediately for the first boundary and only waits when a second
one arrives while the first is still pending. Shutdown still drains, because no
slice will run a queued boundary once the queue stops accepting work, and a
cancelled queue drops pending boundaries along with the rest.
Measured on Octopath Traveler II: the call went from 223 ms to 72 ms, and the
guest render thread spent 38 s instead of 107 s of its 170 s inside it.
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