Yielding At Nine Milliseconds

An MLFQ has three queues and a 10 ms allotment at every level, running the original rules 4a and 4b: a job that uses its whole allotment drops a level, and a job that gives up the CPU before the allotment expires stays at its level with the allotment reset. There is no priority boost.

Two jobs share the CPU:

Job Behaviour
A Pure CPU. Never blocks.
B Runs 9 ms of CPU, issues a 1 ms disk read, repeats forever.

Once the system settles, what share of the CPU does A get?

A

90 percent. B spends most of its cycle waiting, so A absorbs the rest

B

About 10 percent, the 1 ms per cycle when B is blocked on its read

C

0 percent. B holds the top queue permanently, so A never runs at all

D

50 percent. Both jobs end up in the bottom queue and share it round-robin