Commit 02a8f01b authored by Justin TerAvest's avatar Justin TerAvest Committed by Jens Axboe

cfq-iosched: Don't wait if queue already has requests.

Commit 7667aa06 added logic to wait for
the last queue of the group to become busy (have at least one request),
so that the group does not lose out for not being continuously
backlogged. The commit did not check for the condition that the last
queue already has some requests. As a result, if the queue already has
requests, wait_busy is set. Later on, cfq_select_queue() checks the
flag, and decides that since the queue has a request now and wait_busy
is set, the queue is expired.  This results in early expiration of the
queue.

This patch fixes the problem by adding a check to see if queue already
has requests. If it does, wait_busy is not set. As a result, time slices
do not expire early.

The queues with more than one request are usually buffered writers.
Testing shows improvement in isolation between buffered writers.

Cc: stable@kernel.org
Signed-off-by: default avatarJustin TerAvest <teravest@google.com>
Reviewed-by: default avatarGui Jianfeng <guijianfeng@cn.fujitsu.com>
Acked-by: default avatarVivek Goyal <vgoyal@redhat.com>
Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
parent be2c6b19
...@@ -3432,6 +3432,10 @@ static bool cfq_should_wait_busy(struct cfq_data *cfqd, struct cfq_queue *cfqq) ...@@ -3432,6 +3432,10 @@ static bool cfq_should_wait_busy(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{ {
struct cfq_io_context *cic = cfqd->active_cic; struct cfq_io_context *cic = cfqd->active_cic;
/* If the queue already has requests, don't wait */
if (!RB_EMPTY_ROOT(&cfqq->sort_list))
return false;
/* If there are other queues in the group, don't wait */ /* If there are other queues in the group, don't wait */
if (cfqq->cfqg->nr_cfqq > 1) if (cfqq->cfqg->nr_cfqq > 1)
return false; return false;
......
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