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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
CONFIG_IOSCHED_AS_HIER. Even with CONFIG_IOSCHED_AS_HIER=y, with-out any
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
  writes.

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
  slice_idle.

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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