linux-kernel - [PATCH v4 3/8] block, bfq: initialize bfqq->decrease_time

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Message-Id: <20230116095153.3810101-4-shikemeng@huaweicloud.com>
Date:   Mon, 16 Jan 2023 17:51:48 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     jack@...e.com, damien.lemoal@...nsource.wdc.com,
        paolo.valente@...aro.org, axboe@...nel.dk
Cc:     hch@....de, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 3/8] block, bfq: initialize bfqq->decrease_time_jif correctly

Inject limit is updated or reset when time_is_before_eq_jiffies(
decrease_time_jif + several msecs) or think-time state changes.
decrease_time_jif is initialized to 0 and will be set to current jiffies
when inject limit is updated or reset. If the jiffies is slightly greater
than LONG_MAX, time_is_after_eq_jiffies(0) will keep for a long time, so as
time_is_after_eq_jiffies(decrease_time_jif + several msecs). If the
think-time state never chages, then the injection will not work as expected
for long time.

To be more specific:
Function bfq_update_inject_limit maybe triggered when jiffies pasts
decrease_time_jif + msecs_to_jiffies(10) in bfq_add_request by setting
bfqd->wait_dispatch to true.
Function bfq_reset_inject_limit are called in two conditions:
1. jiffies pasts bfqq->decrease_time_jif + msecs_to_jiffies(1000) in
function bfq_add_request.
2. jiffies pasts bfqq->decrease_time_jif + msecs_to_jiffies(100) or
bfq think-time state change from short to long.

Fix this by initializing bfqq->decrease_time_jif to current jiffies
to trigger service injection soon when service injection conditions
are met.

Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
Reviewed-by: Jan Kara <jack@...e.cz>
---
 block/bfq-iosched.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index f038b4d16d86..698c5918ad10 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5654,6 +5654,8 @@ static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,

 	/* first request is almost certainly seeky */
 	bfqq->seek_history = 1;
+
+	bfqq->decrease_time_jif = jiffies;
 }

 static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
-- 
2.30.0