[PATCH BUGFIX/IMPROVEMENT 3/6] block, bfq: make shared queues inherit wakers

Paolo Valente
2021-01-26T10:52:57Z

Consider a bfq_queue bfqq that is about to be merged with another
bfq_queue new_bfqq. The processes associated with bfqq are cooperators
of the processes associated with new_bfqq. So, if bfqq has a waker,
then it is reasonable (and beneficial for throughput) to assume that
all these processes will be happy to let bfqq's waker freely inject
I/O when they have no I/O. So this commit makes new_bfqq inherit
bfqq's waker.

Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
---
block/bfq-iosched.c | 42 +++++++++++++++++++++++++++++++++++++++---
1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index e5b83910fbe0..c5bda33c0923 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2819,6 +2819,29 @@ bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
bfq_mark_bfqq_IO_bound(new_bfqq);
bfq_clear_bfqq_IO_bound(bfqq);

+ /*
+ * The processes associated with bfqq are cooperators of the
+ * processes associated with new_bfqq. So, if bfqq has a
+ * waker, then assume that all these processes will be happy
+ * to let bfqq's waker freely inject I/O when they have no
+ * I/O.
+ */
+ if (bfqq->waker_bfqq && !new_bfqq->waker_bfqq &&
+ bfqq->waker_bfqq != new_bfqq) {
+ new_bfqq->waker_bfqq = bfqq->waker_bfqq;
+ new_bfqq->tentative_waker_bfqq = NULL;
+
+ /*
+ * If the waker queue disappears, then
+ * new_bfqq->waker_bfqq must be reset. So insert
+ * new_bfqq into the woken_list of the waker. See
+ * bfq_check_waker for details.
+ */
+ hlist_add_head(&new_bfqq->woken_list_node,
+ &new_bfqq->waker_bfqq->woken_list);
+
+ }
+
/*
* If bfqq is weight-raised, then let new_bfqq inherit
* weight-raising. To reduce false positives, neglect the case
@@ -6276,7 +6299,7 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
if (likely(!new_queue)) {
/* If the queue was seeky for too long, break it apart. */
if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq)) {
- bfq_log_bfqq(bfqd, bfqq, "breaking apart bfqq");
+ struct bfq_queue *old_bfqq = bfqq;

/* Update bic before losing reference to bfqq */
if (bfq_bfqq_in_large_burst(bfqq))
@@ -6285,11 +6308,24 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
bfqq = bfq_split_bfqq(bic, bfqq);
split = true;

- if (!bfqq)
+ if (!bfqq) {
bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
true, is_sync,
NULL);
- else
+ bfqq->waker_bfqq = old_bfqq->waker_bfqq;
+ bfqq->tentative_waker_bfqq = NULL;
+
+ /*
+ * If the waker queue disappears, then
+ * new_bfqq->waker_bfqq must be
+ * reset. So insert new_bfqq into the
+ * woken_list of the waker. See
+ * bfq_check_waker for details.
+ */
+ if (bfqq->waker_bfqq)
+ hlist_add_head(&bfqq->woken_list_node,
+ &bfqq->waker_bfqq->woken_list);
+ } else
bfqq_already_existing = true;
}
}
--
2.20.1