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Subject[PATCH] CFQ:optimize the cfq_should_preempt()

The patch don't fix bug, just optimizes the cfq_should_preempt()
to preempt higher priority queue.

Additionally, the comment above cfq_preempt_queue() is outdated.


Signed-off-by: Shan Wei <shanwei@cn.fujitsu.com>
---
block/cfq-iosched.c | 17 +++++------------
1 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index a55a9bd..427f522 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1993,10 +1993,10 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
if (cfq_slice_used(cfqq))
return 1;

- if (cfq_class_idle(new_cfqq))
- return 0;
-
- if (cfq_class_idle(cfqq))
+ /*
+ * if new_cfqq is of higher priority, preempting the active queue.
+ */
+ if (new_cfqq->ioprio_class < cfqq->ioprio_class)
return 1;

/*
@@ -2013,12 +2013,6 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
if (rq_is_meta(rq) && !cfqq->meta_pending)
return 1;

- /*
- * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
- */
- if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
- return 1;
-
if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))
return 0;

@@ -2033,8 +2027,7 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
}

/*
- * cfqq preempts the active queue. if we allowed preempt with no slice left,
- * let it have half of its nominal slice.
+ * cfqq preempts the active queue, and is set a new slice time.
*/
static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{

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