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authorJustin TerAvest <teravest@google.com>2011-02-09 13:20:03 (GMT)
committerJens Axboe <jaxboe@fusionio.com>2011-02-09 13:22:36 (GMT)
commit02a8f01b5a9f396d0327977af4c232d0f94c45fd (patch)
treeace818b81f26c30c473af698882dc9786d13afe5
parentbe2c6b1990904dbd43f3d9b90fa2c530504375cd (diff)
cfq-iosched: Don't wait if queue already has requests.
Commit 7667aa0630407bc07dc38dcc79d29cc0a65553c1 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: Justin TerAvest <teravest@google.com> Reviewed-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com> Acked-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
-rw-r--r--block/cfq-iosched.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index ace16865..7be4c79 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -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;
+ /* 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 (cfqq->cfqg->nr_cfqq > 1)
return false;

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