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blk-throttle: Move service tree validation out of the throtl_rb_first() 

The throtl_schedule_next_dispatch() will validate if the service queue
is empty before calling update_min_dispatch_time(), and the
update_min_dispatch_time() will call throtl_rb_first(), which will
validate service queue again.

Thus we can move the service queue validation out of the
throtl_rb_first() to remove the redundant validation in the fast path.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Baolin Wang 2020-10-08 11:52:27 +08:00 committed by Jens Axboe
parent b7b609de5a
commit 2397611ac8
1 changed files with 5 additions and 4 deletions
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9
block/blk-throttle.c
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@ -638,9 +638,6 @@ static struct throtl_grp *
throtl_rb_first(struct throtl_service_queue *parent_sq)
{
struct rb_node *n;
/* Service tree is empty */
if (!parent_sq->nr_pending)
return NULL;
n = rb_first_cached(&parent_sq->pending_tree);
WARN_ON_ONCE(!n);
@ -1224,9 +1221,13 @@ static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
unsigned int nr_disp = 0;
while (1) {
struct throtl_grp *tg = throtl_rb_first(parent_sq);
struct throtl_grp *tg;
struct throtl_service_queue *sq;
if (!parent_sq->nr_pending)
break;
tg = throtl_rb_first(parent_sq);
if (!tg)
break;