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Subject[PATCH 14/21] blkio: Provide some isolation between groups
Date
o Do not allow following three operations across groups for isolation.
- selection of co-operating queues
- preemtpions across groups
- request merging across groups.

o Async queues are currently global and not per group. Allow preemption of
an async queue if a sync queue in other group gets backlogged.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
block/cfq-iosched.c | 30 ++++++++++++++++++++----------
1 files changed, 20 insertions(+), 10 deletions(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 8abc25b..ed18746 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1463,6 +1463,9 @@ static int cfq_allow_merge(struct request_queue *q, struct request *rq,
struct cfq_io_context *cic;
struct cfq_queue *cfqq;

+ /* Deny merge if bio and rq don't belong to same cfq group */
+ if ((RQ_CFQQ(rq))->cfqg != cfq_get_cfqg(cfqd, 0))
+ return false;
/*
* Disallow merge of a sync bio into an async request.
*/
@@ -1700,6 +1703,10 @@ static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd,
if (!cfqq)
return NULL;

+ /* If new queue belongs to different cfq_group, don't choose it */
+ if (cur_cfqq->cfqg != cfqq->cfqg)
+ return NULL;
+
/*
* It only makes sense to merge sync queues.
*/
@@ -2952,22 +2959,12 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
if (!cfqq)
return false;

- if (cfq_slice_used(cfqq))
- return true;
-
if (cfq_class_idle(new_cfqq))
return false;

if (cfq_class_idle(cfqq))
return true;

- /* Allow preemption only if we are idling on sync-noidle tree */
- if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD &&
- cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD &&
- new_cfqq->service_tree->count == 2 &&
- RB_EMPTY_ROOT(&cfqq->sort_list))
- return true;
-
/*
* if the new request is sync, but the currently running queue is
* not, let the sync request have priority.
@@ -2975,6 +2972,19 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
return true;

+ if (new_cfqq->cfqg != cfqq->cfqg)
+ return false;
+
+ if (cfq_slice_used(cfqq))
+ return true;
+
+ /* Allow preemption only if we are idling on sync-noidle tree */
+ if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD &&
+ cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD &&
+ new_cfqq->service_tree->count == 2 &&
+ RB_EMPTY_ROOT(&cfqq->sort_list))
+ return true;
+
/*
* 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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