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-rw-r--r--block/bfq-iosched.c57
-rw-r--r--block/bfq-iosched.h2
-rw-r--r--block/bfq-wf2q.c4
3 files changed, 52 insertions, 11 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 2cf395daee80..7066d90f09df 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -166,6 +166,20 @@ static const int bfq_async_charge_factor = 10;
/* Default timeout values, in jiffies, approximating CFQ defaults. */
const int bfq_timeout = HZ / 8;
+/*
+ * Time limit for merging (see comments in bfq_setup_cooperator). Set
+ * to the slowest value that, in our tests, proved to be effective in
+ * removing false positives, while not causing true positives to miss
+ * queue merging.
+ *
+ * As can be deduced from the low time limit below, queue merging, if
+ * successful, happens at the very beggining of the I/O of the involved
+ * cooperating processes, as a consequence of the arrival of the very
+ * first requests from each cooperator. After that, there is very
+ * little chance to find cooperators.
+ */
+static const unsigned long bfq_merge_time_limit = HZ/10;
+
static struct kmem_cache *bfq_pool;
/* Below this threshold (in ns), we consider thinktime immediate. */
@@ -444,6 +458,13 @@ bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root,
return bfqq;
}
+static bool bfq_too_late_for_merging(struct bfq_queue *bfqq)
+{
+ return bfqq->service_from_backlogged > 0 &&
+ time_is_before_jiffies(bfqq->first_IO_time +
+ bfq_merge_time_limit);
+}
+
void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
struct rb_node **p, *parent;
@@ -454,6 +475,14 @@ void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
bfqq->pos_root = NULL;
}
+ /*
+ * bfqq cannot be merged any longer (see comments in
+ * bfq_setup_cooperator): no point in adding bfqq into the
+ * position tree.
+ */
+ if (bfq_too_late_for_merging(bfqq))
+ return;
+
if (bfq_class_idle(bfqq))
return;
if (!bfqq->next_rq)
@@ -1935,6 +1964,9 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
struct bfq_queue *new_bfqq)
{
+ if (bfq_too_late_for_merging(new_bfqq))
+ return false;
+
if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) ||
(bfqq->ioprio_class != new_bfqq->ioprio_class))
return false;
@@ -2003,6 +2035,20 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
{
struct bfq_queue *in_service_bfqq, *new_bfqq;
+ /*
+ * Prevent bfqq from being merged if it has been created too
+ * long ago. The idea is that true cooperating processes, and
+ * thus their associated bfq_queues, are supposed to be
+ * created shortly after each other. This is the case, e.g.,
+ * for KVM/QEMU and dump I/O threads. Basing on this
+ * assumption, the following filtering greatly reduces the
+ * probability that two non-cooperating processes, which just
+ * happen to do close I/O for some short time interval, have
+ * their queues merged by mistake.
+ */
+ if (bfq_too_late_for_merging(bfqq))
+ return NULL;
+
if (bfqq->new_bfqq)
return bfqq->new_bfqq;
@@ -3003,17 +3049,6 @@ void bfq_bfqq_expire(struct bfq_data *bfqd,
slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta);
/*
- * Increase service_from_backlogged before next statement,
- * because the possible next invocation of
- * bfq_bfqq_charge_time would likely inflate
- * entity->service. In contrast, service_from_backlogged must
- * contain real service, to enable the soft real-time
- * heuristic to correctly compute the bandwidth consumed by
- * bfqq.
- */
- bfqq->service_from_backlogged += entity->service;
-
- /*
* As above explained, charge slow (typically seeky) and
* timed-out queues with the time and not the service
* received, to favor sequential workloads.
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 91c4390903a1..5d47b58d5fc8 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -344,6 +344,8 @@ struct bfq_queue {
unsigned long wr_start_at_switch_to_srt;
unsigned long split_time; /* time of last split */
+
+ unsigned long first_IO_time; /* time of first I/O for this queue */
};
/**
diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
index e495d3f9b4b0..4456eda34e48 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -835,6 +835,10 @@ void bfq_bfqq_served(struct bfq_queue *bfqq, int served)
struct bfq_entity *entity = &bfqq->entity;
struct bfq_service_tree *st;
+ if (!bfqq->service_from_backlogged)
+ bfqq->first_IO_time = jiffies;
+
+ bfqq->service_from_backlogged += served;
for_each_entity(entity) {
st = bfq_entity_service_tree(entity);