[PATCH BUGFIX/IMPROVEMENT V2 1/3] block, bfq: make lookup_next_entity push up vtime on expirations

To provide a very smooth service, bfq starts to serve a bfq_queue only if the queue is 'eligible', i.e., if the same queue would have started to be served in the ideal, perfectly fair system that bfq simulates internally. This is obtained by associating each queue with a virtual start time, and by

[PATCH BUGFIX/IMPROVEMENT V2 1/3] block, bfq: make lookup_next_entity push up vtime on expirations

To provide a very smooth service, bfq starts to serve a bfq_queue only if the queue is 'eligible', i.e., if the same queue would have started to be served in the ideal, perfectly fair system that bfq simulates internally. This is obtained by associating each queue with a virtual start time, and by