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[dm-devel] Re: [PATCH 17/23] io-controller: anticipatory changes for hierarchical fair queuing

Vivek Goyal wrote:
This patch changes anticipatory scheduler to use queue scheduling code from
elevator layer.  One can go back to old as by deselecting
other cgroup created, AS behavior should remain the same as old.

o AS is a single queue ioschduler, that means there is one AS queue per group.

o common layer code select the queue to dispatch from based on fairness, and
  then AS code selects the request with-in group.

o AS runs reads and writes batches with-in group. So common layer runs timed
  group queues and with-in group time, AS runs timed batches of reads and

o Note: Previously AS write batch length was adjusted synamically whenever
  a W->R batch data direction took place and when first request from the
  read batch completed.

  Now write batch updation takes place when last request from the write
  batch has finished during W->R transition.

o AS runs its own anticipation logic to anticipate on reads. common layer also
  does the anticipation on the group if think time of the group is with-in

o Introduced few debugging messages in AS.

Signed-off-by: Nauman Rafique <nauman google com>
Signed-off-by: Vivek Goyal <vgoyal redhat com>

Acked-by: Rik van Riel <riel redhat com>

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