[PATCH 7/8] bfq: Log waker detections

Jan Kara
2021-10-06T17:32:08Z

Waker - wakee relationships are important in deciding whether one queue
can preempt the other one. Print information about detected waker-wakee
relationships so that scheduling decisions can be better understood from
block traces.

Signed-off-by: Jan Kara <jack@suse.cz>
---
block/bfq-iosched.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 6c5e9bafdb5d..886befc35b57 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2127,6 +2127,8 @@ static void bfq_update_io_intensity(struct bfq_queue *bfqq, u64 now_ns)
static void bfq_check_waker(struct bfq_data *bfqd, struct bfq_queue *bfqq,
u64 now_ns)
{
+ char waker_name[MAX_BFQQ_NAME_LENGTH];
+
if (!bfqd->last_completed_rq_bfqq ||
bfqd->last_completed_rq_bfqq == bfqq ||
bfq_bfqq_has_short_ttime(bfqq) ||
@@ -2154,12 +2156,18 @@ static void bfq_check_waker(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bfqd->last_completed_rq_bfqq;
bfqq->num_waker_detections = 1;
bfqq->waker_detection_started = now_ns;
+ bfq_bfqq_name(bfqq->tentative_waker_bfqq, waker_name,
+ MAX_BFQQ_NAME_LENGTH);
+ bfq_log_bfqq(bfqd, bfqq, "set tenative waker %s", waker_name);
} else /* Same tentative waker queue detected again */
bfqq->num_waker_detections++;

if (bfqq->num_waker_detections == 3) {
bfqq->waker_bfqq = bfqd->last_completed_rq_bfqq;
bfqq->tentative_waker_bfqq = NULL;
+ bfq_bfqq_name(bfqq->waker_bfqq, waker_name,
+ MAX_BFQQ_NAME_LENGTH);
+ bfq_log_bfqq(bfqd, bfqq, "set waker %s", waker_name);

/*
* If the waker queue disappears, then
--
2.26.2