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

From: Rik van Riel
Date: Sat Aug 29 2009 - 20:39:17 EST

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@xxxxxxxxxx>

Acked-by: Rik van Riel <riel@xxxxxxxxxx>

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