[PATCH 4/4] blkio: Recalculate the throttled bio dispatch time upon throttle limit change
From: Vivek Goyal
Date: Tue Sep 28 2010 - 13:11:49 EST
o Currently any cgroup throttle limit changes are processed asynchronousy and
the change does not take affect till a new bio is dispatched from same group.
o It might happen that a user sets a redicuously low limit on throttling.
Say 1 bytes per second on reads. In such cases simple operations like mount
a disk can wait for a very long time.
o Once bio is throttled, there is no easy way to come out of that wait even if
user increases the read limit later.
o This patch fixes it. Now if a user changes the cgroup limits, we recalculate
the bio dispatch time according to new limits.
o Can't take queueu lock under blkcg_lock, hence after the change I wake
up the dispatch thread again which recalculates the time. So there are some
variables being synchronized across two threads without lock and I had to
make use of barriers. Hoping I have used barriers correctly. Any review of
memory barrier code especially will help.
Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
---
block/blk-cgroup.c | 15 ++++--
block/blk-cgroup.h | 21 ++++----
block/blk-throttle.c | 134 +++++++++++++++++++++++++++++++++++++++++++-------
block/cfq-iosched.c | 4 +-
4 files changed, 139 insertions(+), 35 deletions(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 357f472..e863418 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -124,7 +124,8 @@ blkio_update_group_weight(struct blkio_group *blkg, unsigned int weight)
if (blkiop->plid != blkg->plid)
continue;
if (blkiop->ops.blkio_update_group_weight_fn)
- blkiop->ops.blkio_update_group_weight_fn(blkg, weight);
+ blkiop->ops.blkio_update_group_weight_fn(blkg->key,
+ blkg, weight);
}
}
@@ -141,11 +142,13 @@ static inline void blkio_update_group_bps(struct blkio_group *blkg, u64 bps,
if (fileid == BLKIO_THROTL_read_bps_device
&& blkiop->ops.blkio_update_group_read_bps_fn)
- blkiop->ops.blkio_update_group_read_bps_fn(blkg, bps);
+ blkiop->ops.blkio_update_group_read_bps_fn(blkg->key,
+ blkg, bps);
if (fileid == BLKIO_THROTL_write_bps_device
&& blkiop->ops.blkio_update_group_write_bps_fn)
- blkiop->ops.blkio_update_group_write_bps_fn(blkg, bps);
+ blkiop->ops.blkio_update_group_write_bps_fn(blkg->key,
+ blkg, bps);
}
}
@@ -162,11 +165,13 @@ static inline void blkio_update_group_iops(struct blkio_group *blkg,
if (fileid == BLKIO_THROTL_read_iops_device
&& blkiop->ops.blkio_update_group_read_iops_fn)
- blkiop->ops.blkio_update_group_read_iops_fn(blkg, iops);
+ blkiop->ops.blkio_update_group_read_iops_fn(blkg->key,
+ blkg, iops);
if (fileid == BLKIO_THROTL_write_iops_device
&& blkiop->ops.blkio_update_group_write_iops_fn)
- blkiop->ops.blkio_update_group_write_iops_fn(blkg,iops);
+ blkiop->ops.blkio_update_group_write_iops_fn(blkg->key,
+ blkg,iops);
}
}
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 2070053..034c355 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -186,16 +186,17 @@ extern unsigned int blkcg_get_write_iops(struct blkio_cgroup *blkcg,
dev_t dev);
typedef void (blkio_unlink_group_fn) (void *key, struct blkio_group *blkg);
-typedef void (blkio_update_group_weight_fn) (struct blkio_group *blkg,
- unsigned int weight);
-typedef void (blkio_update_group_read_bps_fn) (struct blkio_group *blkg,
- u64 read_bps);
-typedef void (blkio_update_group_write_bps_fn) (struct blkio_group *blkg,
- u64 write_bps);
-typedef void (blkio_update_group_read_iops_fn) (struct blkio_group *blkg,
- unsigned int read_iops);
-typedef void (blkio_update_group_write_iops_fn) (struct blkio_group *blkg,
- unsigned int write_iops);
+
+typedef void (blkio_update_group_weight_fn) (void *key,
+ struct blkio_group *blkg, unsigned int weight);
+typedef void (blkio_update_group_read_bps_fn) (void * key,
+ struct blkio_group *blkg, u64 read_bps);
+typedef void (blkio_update_group_write_bps_fn) (void *key,
+ struct blkio_group *blkg, u64 write_bps);
+typedef void (blkio_update_group_read_iops_fn) (void *key,
+ struct blkio_group *blkg, unsigned int read_iops);
+typedef void (blkio_update_group_write_iops_fn) (void *key,
+ struct blkio_group *blkg, unsigned int write_iops);
struct blkio_policy_ops {
blkio_unlink_group_fn *blkio_unlink_group_fn;
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index bc2936b..11713ed 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -70,6 +70,9 @@ struct throtl_grp {
/* When did we start a new slice */
unsigned long slice_start[2];
unsigned long slice_end[2];
+
+ /* Some throttle limits got updated for the group */
+ bool limits_changed;
};
struct throtl_data
@@ -93,6 +96,8 @@ struct throtl_data
/* Work for dispatching throttled bios */
struct delayed_work throtl_work;
+
+ atomic_t limits_changed;
};
enum tg_state_flags {
@@ -592,15 +597,6 @@ static void tg_update_disptime(struct throtl_data *td, struct throtl_grp *tg)
min_wait = min(read_wait, write_wait);
disptime = jiffies + min_wait;
- /*
- * If group is already on active tree, then update dispatch time
- * only if it is lesser than existing dispatch time. Otherwise
- * always update the dispatch time
- */
-
- if (throtl_tg_on_rr(tg) && time_before(disptime, tg->disptime))
- return;
-
/* Update dispatch time */
throtl_dequeue_tg(td, tg);
tg->disptime = disptime;
@@ -691,6 +687,46 @@ static int throtl_select_dispatch(struct throtl_data *td, struct bio_list *bl)
return nr_disp;
}
+static void throtl_process_limit_change(struct throtl_data *td)
+{
+ struct throtl_grp *tg;
+ struct hlist_node *pos, *n;
+
+ /*
+ * Make sure atomic_inc() effects from
+ * throtl_update_blkio_group_read_bps(), group of functions are
+ * visible.
+ * Is this required or smp_mb__after_atomic_inc() was suffcient
+ * after the atomic_inc().
+ */
+ smp_rmb();
+ if (!atomic_read(&td->limits_changed))
+ return;
+
+ throtl_log(td, "limit changed =%d", atomic_read(&td->limits_changed));
+
+ hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
+ /*
+ * Do I need an smp_rmb() here to make sure tg->limits_changed
+ * update is visible. I am relying on smp_rmb() at the
+ * beginning of function and not putting a new one here.
+ */
+
+ if (throtl_tg_on_rr(tg) && tg->limits_changed) {
+ throtl_log_tg(td, tg, "limit change rbps=%llu wbps=%llu"
+ " riops=%u wiops=%u", tg->bps[READ],
+ tg->bps[WRITE], tg->iops[READ],
+ tg->iops[WRITE]);
+ tg_update_disptime(td, tg);
+ tg->limits_changed = false;
+ }
+ }
+
+ smp_mb__before_atomic_dec();
+ atomic_dec(&td->limits_changed);
+ smp_mb__after_atomic_dec();
+}
+
/* Dispatch throttled bios. Should be called without queue lock held. */
static int throtl_dispatch(struct request_queue *q)
{
@@ -701,6 +737,8 @@ static int throtl_dispatch(struct request_queue *q)
spin_lock_irq(q->queue_lock);
+ throtl_process_limit_change(td);
+
if (!total_nr_queued(td))
goto out;
@@ -821,28 +859,74 @@ void throtl_unlink_blkio_group(void *key, struct blkio_group *blkg)
spin_unlock_irqrestore(td->queue->queue_lock, flags);
}
-static void throtl_update_blkio_group_read_bps (struct blkio_group *blkg,
- u64 read_bps)
+/*
+ * For all update functions, key should be a valid pointer because these
+ * update functions are called under blkcg_lock, that means, blkg is
+ * valid and in turn key is valid. queue exit path can not race becuase
+ * of blkcg_lock
+ *
+ * Can not take queue lock in update functions as queue lock under blkcg_lock
+ * is not allowed. Under other paths we take blkcg_lock under queue_lock.
+ */
+static void throtl_update_blkio_group_read_bps(void *key,
+ struct blkio_group *blkg, u64 read_bps)
{
+ struct throtl_data *td = key;
+
tg_of_blkg(blkg)->bps[READ] = read_bps;
+ /* Make sure read_bps is updated before setting limits_changed */
+ smp_wmb();
+ tg_of_blkg(blkg)->limits_changed = true;
+
+ /* Make sure tg->limits_changed is updated before td->limits_changed */
+ smp_mb__before_atomic_inc();
+ atomic_inc(&td->limits_changed);
+ smp_mb__after_atomic_inc();
+
+ /* Schedule a work now to process the limit change */
+ throtl_schedule_delayed_work(td->queue, 0);
}
-static void throtl_update_blkio_group_write_bps (struct blkio_group *blkg,
- u64 write_bps)
+static void throtl_update_blkio_group_write_bps(void *key,
+ struct blkio_group *blkg, u64 write_bps)
{
+ struct throtl_data *td = key;
+
tg_of_blkg(blkg)->bps[WRITE] = write_bps;
+ smp_wmb();
+ tg_of_blkg(blkg)->limits_changed = true;
+ smp_mb__before_atomic_inc();
+ atomic_inc(&td->limits_changed);
+ smp_mb__after_atomic_inc();
+ throtl_schedule_delayed_work(td->queue, 0);
}
-static void throtl_update_blkio_group_read_iops (struct blkio_group *blkg,
- unsigned int read_iops)
+static void throtl_update_blkio_group_read_iops(void *key,
+ struct blkio_group *blkg, unsigned int read_iops)
{
+ struct throtl_data *td = key;
+
tg_of_blkg(blkg)->iops[READ] = read_iops;
+ smp_wmb();
+ tg_of_blkg(blkg)->limits_changed = true;
+ smp_mb__before_atomic_inc();
+ atomic_inc(&td->limits_changed);
+ smp_mb__after_atomic_inc();
+ throtl_schedule_delayed_work(td->queue, 0);
}
-static void throtl_update_blkio_group_write_iops (struct blkio_group *blkg,
- unsigned int write_iops)
+static void throtl_update_blkio_group_write_iops(void *key,
+ struct blkio_group *blkg, unsigned int write_iops)
{
+ struct throtl_data *td = key;
+
tg_of_blkg(blkg)->iops[WRITE] = write_iops;
+ smp_wmb();
+ tg_of_blkg(blkg)->limits_changed = true;
+ smp_mb__before_atomic_inc();
+ atomic_inc(&td->limits_changed);
+ smp_mb__after_atomic_inc();
+ throtl_schedule_delayed_work(td->queue, 0);
}
void throtl_shutdown_timer_wq(struct request_queue *q)
@@ -886,8 +970,14 @@ int blk_throtl_bio(struct request_queue *q, struct bio **biop)
/*
* There is already another bio queued in same dir. No
* need to update dispatch time.
+ * Still update the disptime if rate limits on this group
+ * were changed.
*/
- update_disptime = false;
+ if (!tg->limits_changed)
+ update_disptime = false;
+ else
+ tg->limits_changed = false;
+
goto queue_bio;
}
@@ -929,6 +1019,7 @@ int blk_throtl_init(struct request_queue *q)
INIT_HLIST_HEAD(&td->tg_list);
td->tg_service_tree = THROTL_RB_ROOT;
+ atomic_set(&td->limits_changed, 0);
/* Init root group */
tg = &td->root_tg;
@@ -996,6 +1087,13 @@ void blk_throtl_exit(struct request_queue *q)
*/
if (wait)
synchronize_rcu();
+
+ /*
+ * Just being safe to make sure after previous flush if some body did
+ * update limits through cgroup and another work got queued, cancel
+ * it.
+ */
+ throtl_shutdown_timer_wq(q);
throtl_td_free(td);
}
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 6db8884..ee9cd3a 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -976,8 +976,8 @@ static inline struct cfq_group *cfqg_of_blkg(struct blkio_group *blkg)
return NULL;
}
-void
-cfq_update_blkio_group_weight(struct blkio_group *blkg, unsigned int weight)
+void cfq_update_blkio_group_weight(void *key, struct blkio_group *blkg,
+ unsigned int weight)
{
cfqg_of_blkg(blkg)->weight = weight;
}
--
1.7.2.3
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