[PATCH 15/20] blkio: Take care of preemptions across groups

[Vivek Goyal]

o Additional preemption checks for groups where we travel up the hierarchy
  and see if one queue should preempt other or not.

o Also prevents preemption across groups in some cases to provide isolation
  between groups.

Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
---
 block/cfq-iosched.c |   33 +++++++++++++++++++++++++++++++++
 1 files changed, 33 insertions(+), 0 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 87b1799..98dbead 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2636,6 +2636,36 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 	}
 }
 
+static bool cfq_should_preempt_group(struct cfq_data *cfqd,
+		struct cfq_queue *cfqq, struct cfq_queue *new_cfqq)
+{
+	struct cfq_entity *cfqe = &cfqq->entity;
+	struct cfq_entity *new_cfqe = &new_cfqq->entity;
+
+	if (cfqq_to_cfqg(cfqq) != &cfqd->root_group)
+		cfqe = parent_entity(&cfqq->entity);
+
+	if (cfqq_to_cfqg(new_cfqq) != &cfqd->root_group)
+		new_cfqe = parent_entity(&new_cfqq->entity);
+
+	/*
+	 * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
+	 */
+
+	if (new_cfqe->ioprio_class == IOPRIO_CLASS_RT
+	    && cfqe->ioprio_class != IOPRIO_CLASS_RT)
+		return true;
+	/*
+	 * Allow an BE request to pre-empt an ongoing IDLE clas timeslice.
+	 */
+
+	if (new_cfqe->ioprio_class == IOPRIO_CLASS_BE
+	    && cfqe->ioprio_class == IOPRIO_CLASS_IDLE)
+		return true;
+
+	return false;
+}
+
 /*
  * Check if new_cfqq should preempt the currently active queue. Return 0 for
  * no or if we aren't sure, a 1 will cause a preempt.
@@ -2666,6 +2696,9 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
 	if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
 		return true;
 
+	if (cfqq_to_cfqg(new_cfqq) != cfqq_to_cfqg(cfqq))
+		return cfq_should_preempt_group(cfqd, cfqq, new_cfqq);
+
 	/*
 	 * So both queues are sync. Let the new request get disk time if
 	 * it's a metadata request and the current queue is doing regular IO.
-- 
1.6.2.5

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