linux-kernel - [PATCH BUGFIX/IMPROVEMENT 3/6] block, bfq: fix switch back from soft-rt weitgh-raising

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Message-Id: <20210125190248.49338-4-paolo.valente@linaro.org>
Date:   Mon, 25 Jan 2021 20:02:45 +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 3/6] block, bfq: fix switch back from soft-rt weitgh-raising

A bfq_queue may happen to be deemed as soft real-time while it is
still enjoying interactive weight-raising. If this happens because of
a false positive, then the bfq_queue is likely to loose its soft
real-time status soon. Upon losing such a status, the bfq_queue must
get back its interactive weight-raising, if its interactive period is
not over yet. But this case is not handled. This commit corrects this
error.

Tested-by: Jan Kara <jack@...e.cz>
Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
---
 block/bfq-iosched.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 6a02a12ff553..9e5242b2788a 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5293,8 +5293,26 @@ bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 
 	if (bfqq->wr_coeff > 1 &&
 	    bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
-	    BFQQ_TOTALLY_SEEKY(bfqq))
-		bfq_bfqq_end_wr(bfqq);
+	    BFQQ_TOTALLY_SEEKY(bfqq)) {
+		if (time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
+					   bfq_wr_duration(bfqd))) {
+			/*
+			 * In soft_rt weight raising with the
+			 * interactive-weight-raising period
+			 * elapsed (so no switch back to
+			 * interactive weight raising).
+			 */
+			bfq_bfqq_end_wr(bfqq);
+		} else { /*
+			  * stopping soft_rt weight raising
+			  * while still in interactive period,
+			  * switch back to interactive weight
+			  * raising
+			  */
+			switch_back_to_interactive_wr(bfqq, bfqd);
+			bfqq->entity.prio_changed = 1;
+		}
+	}
 }
 
 static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
-- 
2.20.1