tg_dispatch_one_bio() currently assumes that the parent_sq is the top
level one and the bio being dispatched is ready to be issued; however,
this assumption will be wrong with proper hierarchy support. This
patch makes the following changes to make tg_dispatch_on_bio() ready
for hiearchy.
* throtl_data->nr_queued[] is incremented in blk_throtl_bio() instead
of throtl_add_bio_tg() so that throtl_add_bio_tg() can be used to
transfer a bio from a child tg to its parent.
* tg_dispatch_one_bio() is updated to distinguish whether its parent
is another throtl_grp or the throtl_data. If former, the bio is
transferred to the parent throtl_grp using throtl_add_bio_tg(). If
latter, the bio is ready to be issued and put on the top-level
service_queue's bio_lists[] and throtl_data->nr_queued is
decremented.
As all throtl_grps currently have the top level service_queue as their
->parent_sq, this patch in itself doesn't make any behavior
difference.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
block/blk-throttle.c | 28 +++++++++++++++++++++-------
1 file changed, 21 insertions(+), 7 deletions(-)
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 99e1e78..367c269 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -821,7 +821,6 @@ static void throtl_add_bio_tg(struct bio *bio, struct throtl_grp *tg)
/* Take a bio reference on tg */
blkg_get(tg_to_blkg(tg));
sq->nr_queued[rw]++;
- tg->td->nr_queued[rw]++;
throtl_enqueue_tg(tg);
}
@@ -852,20 +851,34 @@ static void tg_update_disptime(struct throtl_grp *tg)
static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
{
struct throtl_service_queue *sq = &tg->service_queue;
+ struct throtl_service_queue *parent_sq = sq->parent_sq;
+ struct throtl_grp *parent_tg = sq_to_tg(parent_sq);
struct bio *bio;
bio = bio_list_pop(&sq->bio_lists[rw]);
sq->nr_queued[rw]--;
- /* Drop bio reference on blkg */
- blkg_put(tg_to_blkg(tg));
-
- BUG_ON(tg->td->nr_queued[rw] <= 0);
- tg->td->nr_queued[rw]--;
throtl_charge_bio(tg, bio);
- bio_list_add(&sq->parent_sq->bio_lists[rw], bio);
+
+ /*
+ * If our parent is another tg, we just need to transfer @bio to
+ * the parent using throtl_add_bio_tg(). If our parent is
+ * @td->service_queue, @bio is ready to be issued. Put it on its
+ * bio_lists[] and decrease total number queued. The caller is
+ * responsible for issuing these bios.
+ */
+ if (parent_tg) {
+ throtl_add_bio_tg(bio, parent_tg);
+ } else {
+ bio_list_add(&parent_sq->bio_lists[rw], bio);
+ BUG_ON(tg->td->nr_queued[rw] <= 0);
+ tg->td->nr_queued[rw]--;
+ }
throtl_trim_slice(tg, rw);
+
+ /* @bio is transferred to parent, drop its blkg reference */
+ blkg_put(tg_to_blkg(tg));
}
static int throtl_dispatch_tg(struct throtl_grp *tg)
@@ -1283,6 +1296,7 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
sq->nr_queued[READ], sq->nr_queued[WRITE]);
bio_associate_current(bio);
+ tg->td->nr_queued[rw]++;
throtl_add_bio_tg(bio, tg);
throttled = true;
--
1.8.1.4
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