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[dm-devel] Re: [PATCH 11/23] io-controller: Introduce group idling

Vivek Goyal wrote:
o It is not always that IO from a process or group is continuous. There are
  cases of dependent reads where next read is not issued till previous read
  has finished. For such cases, CFQ introduced the notion of slice_idle,
  where we idle on the queue for sometime hoping next request will come
  and that's how fairness is provided otherwise queue will be deleted
  immediately from the service tree and this process will not get the
  fair share.

o This patch introduces the similar concept at group level. Idle on the group
  for a period of "group_idle" which is tunable through sysfs interface. So
  if a group is empty and about to be deleted, we idle for the next request.

o This patch also introduces the notion of wait busy where we wait for one
  extra group_idle period even if queue has consumed its time slice. The
  reason being that group will loose its share upon removal from service
  tree as some other entity will be picked for dispatch and vtime jump will
  take place.

Signed-off-by: Vivek Goyal <vgoyal redhat com>

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

All rights reversed.

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