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authorVivek Goyal <vgoyal@redhat.com>2010-10-01 14:49:49 +0200
committerJens Axboe <jaxboe@fusionio.com>2010-10-01 14:49:49 +0200
commitfe0714377ee2ca161bf2afb7773e22f15f1786d4 (patch)
tree09f5e8686d741d012333c92251b8cc66793ef916 /block/blk-throttle.c
parent02977e4af7ed3b478c505e50491ffdf3e1314cf4 (diff)
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blkio: Recalculate the throttled bio dispatch time upon throttle limit change
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@redhat.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Diffstat (limited to 'block/blk-throttle.c')
-rw-r--r--block/blk-throttle.c134
1 files changed, 116 insertions, 18 deletions
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index bc2936b80ad..11713ed852f 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);
}