[dm-devel] [PATCH] io-controller: Preempt a non-rt queue if a rt ioq is present in ancestor or sibling groups

[Gui Jianfeng]

Preempt the ongoing non-rt ioq if there are rt ioqs waiting for dispatching
in ancestor or sibling groups. It will give other group's rt ioq an chance 
to dispatch ASAP.

Signed-off-by: Gui Jianfeng <guijianfeng at cn.fujitsu.com>
---
 block/elevator-fq.c |   44 +++++++++++++++++++++++++++++++++++++++-----
 block/elevator-fq.h |    1 +
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/block/elevator-fq.c b/block/elevator-fq.c
index 2ad40eb..80526fd 100644
--- a/block/elevator-fq.c
+++ b/block/elevator-fq.c
@@ -3245,8 +3245,16 @@ void elv_add_ioq_busy(struct elv_fq_data *efqd, struct io_queue *ioq)
 	elv_mark_ioq_busy(ioq);
 	efqd->busy_queues++;
 	if (elv_ioq_class_rt(ioq)) {
+		struct io_entity *entity;
 		struct io_group *iog = ioq_to_io_group(ioq);
+
 		iog->busy_rt_queues++;
+		entity = iog->entity.parent;
+
+		for_each_entity(entity) {
+			iog = io_entity_to_iog(entity);
+			iog->sub_busy_rt_queues++;
+		}
 	}
 
 #ifdef CONFIG_DEBUG_GROUP_IOSCHED
@@ -3290,9 +3298,18 @@ void elv_del_ioq_busy(struct elevator_queue *e, struct io_queue *ioq,
 	elv_clear_ioq_busy(ioq);
 	BUG_ON(efqd->busy_queues == 0);
 	efqd->busy_queues--;
+
 	if (elv_ioq_class_rt(ioq)) {
+		struct io_entity *entity;
 		struct io_group *iog = ioq_to_io_group(ioq);
+
 		iog->busy_rt_queues--;
+		entity = iog->entity.parent;
+
+		for_each_entity(entity) {
+			iog = io_entity_to_iog(entity);
+			iog->sub_busy_rt_queues--;
+		}
 	}
 
 	elv_deactivate_ioq(efqd, ioq, requeue);
@@ -3735,12 +3752,32 @@ int elv_iosched_expire_ioq(struct request_queue *q, int slice_expired,
 	return ret;
 }
 
+static int check_rt_queue(struct io_queue *ioq)
+{
+	struct io_group *iog;
+	struct io_entity *entity;
+
+	iog = ioq_to_io_group(ioq);
+
+	if (iog->busy_rt_queues)
+		return 1;
+
+	entity = iog->entity.parent;
+
+	for_each_entity(entity) {
+		iog = io_entity_to_iog(entity);
+		if (iog->sub_busy_rt_queues)
+			return 1;
+	}
+
+	return 0;
+}
+
 /* Common layer function to select the next queue to dispatch from */
 void *elv_fq_select_ioq(struct request_queue *q, int force)
 {
 	struct elv_fq_data *efqd = &q->elevator->efqd;
 	struct io_queue *new_ioq = NULL, *ioq = elv_active_ioq(q->elevator);
-	struct io_group *iog;
 	int slice_expired = 1;
 
 	if (!elv_nr_busy_ioq(q->elevator))
@@ -3811,12 +3848,9 @@ void *elv_fq_select_ioq(struct request_queue *q, int force)
 	/*
 	 * If we have a RT cfqq waiting, then we pre-empt the current non-rt
 	 * cfqq.
-	 *
-	 * TODO: This does not seem right across the io groups. Fix it.
 	 */
-	iog = ioq_to_io_group(ioq);
 
-	if (!elv_ioq_class_rt(ioq) && iog->busy_rt_queues) {
+	if (!elv_ioq_class_rt(ioq) && check_rt_queue(ioq)) {
 		/*
 		 * We simulate this as cfqq timed out so that it gets to bank
 		 * the remaining of its time slice.
diff --git a/block/elevator-fq.h b/block/elevator-fq.h
index b3193f8..be6c1af 100644
--- a/block/elevator-fq.h
+++ b/block/elevator-fq.h
@@ -248,6 +248,7 @@ struct io_group {
 	 * non-RT cfqq in service when this value is non-zero.
 	 */
 	unsigned int busy_rt_queues;
+	unsigned int sub_busy_rt_queues;
 
 	int deleting;
 	unsigned short iocg_id;
-- 
1.5.4.rc3