[PATCH 29/31] blk-throttle: make throtl_pending_timer_fn() ready for hierarchy

From: Tejun Heo
Date: Wed May 01 2013 - 20:41:29 EST


throtl_pending_timer_fn() currently assumes that the parent_sq is the
top level one and the bio's dispatched are ready to be issued;
however, this assumption will be wrong with proper hierarchy support.
This patch makes the following changes to make
throtl_pending_timer_fn() ready for hiearchy.

* If the parent_sq isn't the top-level one, update the parent
throtl_grp's dispatch time and schedule the next dispatch as
necessary. If the parent's dispatch time is now, repeat the
function for the parent throtl_grp.

* If the parent_sq is the top-level one, kick issue work_item as
before.

* The debug message printed by throtl_log() now prints out the
service_queue's nr_queued[] instead of the total nr_queued as the
latter becomes uninteresting and misleading with hierarchical
dispatch.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
block/blk-throttle.c | 40 +++++++++++++++++++++++++++++++++-------
1 file changed, 33 insertions(+), 7 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 367c269..f3bd278 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -949,23 +949,33 @@ static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
* This timer is armed when a child throtl_grp with active bio's become
* pending and queued on the service_queue's pending_tree and expires when
* the first child throtl_grp should be dispatched. This function
- * dispatches bio's from the children throtl_grps and kicks
- * throtl_data->dispatch_work if there are bio's ready to be issued.
+ * dispatches bio's from the children throtl_grps to the parent
+ * service_queue.
+ *
+ * If the parent's parent is another throtl_grp, dispatching is propagated
+ * by either arming its pending_timer or repeating dispatch directly. If
+ * the top-level service_tree is reached, throtl_data->dispatch_work is
+ * kicked so that the ready bio's are issued.
*/
static void throtl_pending_timer_fn(unsigned long arg)
{
struct throtl_service_queue *sq = (void *)arg;
+ struct throtl_grp *tg = sq_to_tg(sq);
struct throtl_data *td = sq_to_td(sq);
struct request_queue *q = td->queue;
- bool dispatched = false;
+ struct throtl_service_queue *parent_sq;
+ bool dispatched;
int ret;

spin_lock_irq(q->queue_lock);
+again:
+ parent_sq = sq->parent_sq;
+ dispatched = false;

while (true) {
throtl_log(sq, "dispatch nr_queued=%u read=%u write=%u",
- td->nr_queued[READ] + td->nr_queued[WRITE],
- td->nr_queued[READ], td->nr_queued[WRITE]);
+ sq->nr_queued[READ] + sq->nr_queued[WRITE],
+ sq->nr_queued[READ], sq->nr_queued[WRITE]);

ret = throtl_select_dispatch(sq);
if (ret) {
@@ -982,9 +992,25 @@ static void throtl_pending_timer_fn(unsigned long arg)
spin_lock_irq(q->queue_lock);
}

- if (dispatched)
- queue_work(kthrotld_workqueue, &td->dispatch_work);
+ if (!dispatched)
+ goto out_unlock;

+ if (parent_sq) {
+ /* @parent_sq is another throl_grp, propagate dispatch */
+ if (tg->flags & THROTL_TG_WAS_EMPTY) {
+ tg_update_disptime(tg);
+ if (!throtl_schedule_next_dispatch(parent_sq, false)) {
+ /* window is already open, repeat dispatching */
+ sq = parent_sq;
+ tg = sq_to_tg(sq);
+ goto again;
+ }
+ }
+ } else {
+ /* reached the top-level, queue issueing */
+ queue_work(kthrotld_workqueue, &td->dispatch_work);
+ }
+out_unlock:
spin_unlock_irq(q->queue_lock);
}

--
1.8.1.4

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