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cfq-iosched: Fix the incorrect timeslice accounting with forced_dispatch 

When CFQ dispatches requests forcefully due to a barrier or changing iosched,
it runs through all cfqq's dispatching requests and then expires each queue.
However, it does not activate a cfqq before flushing its IOs resulting in
using stale values for computing slice_used.
This patch fixes it by calling activate queue before flushing reuqests from
each queue.

This is useful mostly for barrier requests because when the iosched is changing
it really doesnt matter if we have incorrect accounting since we're going to
break down all structures anyway.

We also now expire the current timeslice before moving on with the dispatch
to accurately account slice used for that cfqq.

Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Divyesh Shah 2010-04-09 09:29:57 +02:00 committed by Jens Axboe
parent 02246c4117
commit 3440c49f5c
1 changed files with 6 additions and 3 deletions
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9
block/cfq-iosched.c
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@ -2205,10 +2205,13 @@ static int cfq_forced_dispatch(struct cfq_data *cfqd)
struct cfq_queue *cfqq;
int dispatched = 0;
while ((cfqq = cfq_get_next_queue_forced(cfqd)) != NULL)
dispatched += __cfq_forced_dispatch_cfqq(cfqq);
/* Expire the timeslice of the current active queue first */
cfq_slice_expired(cfqd, 0);
while ((cfqq = cfq_get_next_queue_forced(cfqd)) != NULL) {
__cfq_set_active_queue(cfqd, cfqq);
dispatched += __cfq_forced_dispatch_cfqq(cfqq);
}
BUG_ON(cfqd->busy_queues);
cfq_log(cfqd, "forced_dispatch=%d", dispatched);