linux-kernel - [PATCH BUGFIX/IMPROVEMENT 4/6] block, bfq: do not raise non-default weights

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Message-Id: <20210122181948.35660-5-paolo.valente@linaro.org>
Date:   Fri, 22 Jan 2021 19:19:46 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Valente <paolo.valente@...aro.org>,
        Jan Kara <jack@...e.cz>
Subject: [PATCH BUGFIX/IMPROVEMENT 4/6] block, bfq: do not raise non-default weights

BFQ heuristics try to detect interactive I/O, and raise the weight of
the queues containing such an I/O. Yet, if also the user changes the
weight of a queue (i.e., the user changes the ioprio of the process
associated with that queue), then it is most likely better to prevent
BFQ heuristics from silently changing the same weight.

Tested-by: Jan Kara <jack@...e.cz>
Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
---
 block/bfq-iosched.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 43e2c39cf7b5..161badb744d6 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -1671,15 +1671,19 @@ static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
 	 * - it is sync,
 	 * - it does not belong to a large burst,
 	 * - it has been idle for enough time or is soft real-time,
-	 * - is linked to a bfq_io_cq (it is not shared in any sense).
+	 * - is linked to a bfq_io_cq (it is not shared in any sense),
+	 * - has a default weight (otherwise we assume the user wanted
+	 *   to control its weight explicitly)
 	 */
 	in_burst = bfq_bfqq_in_large_burst(bfqq);
 	soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
 		!BFQQ_TOTALLY_SEEKY(bfqq) &&
 		!in_burst &&
 		time_is_before_jiffies(bfqq->soft_rt_next_start) &&
-		bfqq->dispatched == 0;
-	*interactive = !in_burst && idle_for_long_time;
+		bfqq->dispatched == 0 &&
+		bfqq->entity.new_weight == 40;
+	*interactive = !in_burst && idle_for_long_time &&
+		bfqq->entity.new_weight == 40;
 	wr_or_deserves_wr = bfqd->low_latency &&
 		(bfqq->wr_coeff > 1 ||
 		 (bfq_bfqq_sync(bfqq) &&
-- 
2.20.1