Revert "block: row: hardcode magic values."

This reverts commit 16fbf37b218c39115b160a40831a658c0079792d.
block: row: Dispatch requests according to their io-priority
This patch implements "application-hints" which is a way the issuing
application can notify the scheduler on the priority of its request.
This is done by setting the io-priority of the request.
This patch reuses an already existing mechanism of io-priorities developed
for CFQ. Please refer to kernel/Documentation/block/ioprio.txt for
usage example and explanations.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
block: row: Idling mechanism re-factoring
At the moment idling in ROW is implemented by delayed work that uses
jiffies granularity which is not very accurate. This patch replaces
current idling mechanism implementation with hrtime API, which gives
nanosecond resolution (instead of jiffies).

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
block: row: Don't notify URGENT if there are un-completed urgent req
When ROW scheduler reports to the block layer that there is an urgent
request pending, the device driver may decide to stop the transmission
of the current request in order to handle the urgent one. If the current
transmitted request is an urgent request - we don't want it to be
stopped.
Due to the above ROW scheduler won't notify of an urgent request if
there are urgent requests in flight.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
block: row: Update initial values of ROW data structures
This patch sets the initial values of internal ROW
parameters.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
[smuckle@codeaurora.org: ported from msm-3.7]
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>
block: row: Re-design urgent request notification mechanism
When ROW scheduler reports to the block layer that there is an urgent
request pending, the device driver may decide to stop the transmission
of the current request in order to handle the urgent one. This is done
in order to reduce the latency of an urgent request. For example:
long WRITE may be stopped to handle an urgent READ.

This patch updates the ROW URGENT notification policy to apply with the
below:

- Don't notify URGENT if there is an un-completed URGENT request in driver
- After notifying that URGENT request is present, the next request
  dispatched is the URGENT one.
- At every given moment only 1 request can be marked as URGENT.
  Independent of it's location (driver or scheduler)

Other changes to URGENT policy:
- Only READ queues are allowed to notify of an URGENT request pending.

CR fix:
If a pending urgent request (A) gets merged with another request (B)
A is removed from scheduler queue but is not removed from
rd->pending_urgent_rq.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
block: blk-core: add printk_ratelimit
On failure of requests the console is flooded with prints,
which result in a watchdog bark.
This patch limits the number of prints to console thus, avoiding
the bark.

Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
block: row: Prevent starvation of regular priority by high priority
At the moment all REGULAR and LOW priority requests are starved as long as
there are HIGH priority requests to dispatch.
This patch prevents the above starvation by setting a starvation limit the
REGULAR\LOW priority requests can tolerate.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
block: row: Update sysfs functions
All ROW (time related) configurable parameters are stored in ms so there
is no need to convert from/to ms when reading/updating them via sysfs.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
block: row: Fix starvation tolerance values
The current starvation tolerance values increase the boot time
since high priority SW requests are delayed by regular priority requests.
In order to overcome this, increase the starvation tolerance values.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
block: urgent: Fix dispatching of URGENT mechanism
There are cases when blk_peek_request is called not from blk_fetch_request
thus the URGENT request may be started but the flag q->dispatched_urgent is
not updated.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
block: drop @tsk from attempt_plug_merge() and explain sync rules
attempt_plug_merge() accesses elevator without holding queue_lock and
may call into ->elevator_bio_merge_fn().  The elvator is guaranteed to
be valid because it's accessed iff the plugged list has requests and
elevator is never exited with live requests, so as long as the
elevator method can deal with unlocked access, this is safe.

Explain the sync rules around attempt_plug_merge() and drop the
unnecessary @tsk parameter.

This patch doesn't introduce any functional change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>