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>

1 files changed, 11 insertions, 10 deletions

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 2070053a30b1..034c35562dba 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;