linux-kernel - [PATCH v2 03/10] block, bfq: initialize bfqq->decrease_time

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Date:   Fri, 16 Dec 2022 19:12:23 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     jack@...e.cz, paolo.valente@...aro.org, tj@...nel.org,
        josef@...icpanda.com, axboe@...nel.dk
Cc:     cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linfeilong@...wei.com,
        liuzhiqiang@...com, shikemeng@...weicloud.com
Subject: [PATCH v2 03/10] 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>
---
 block/bfq-iosched.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 5a6d9e8c329d..9441fc98961a 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5491,6 +5491,8 @@ 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