From ed3a1d13e8dd5dfd3b309a7ca72996fa49bbfd22 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Thu, 4 Jun 2020 18:07:21 +0200
Subject: bfq: Use only idle IO periods for think time calculations
Patch-mainline: v5.12-rc1
Git-commit: 7684fbde45169e6de15c180b1c084d2005e99961
References: bsc#1171513

Currently whenever bfq queue has a request queued we add now -
last_completion_time to the think time statistics. This is however
misleading in case the process is able to submit several requests in
parallel because e.g. if the queue has request completed at time T0 and
then queues new requests at times T1, T2, then we will add T1-T0 and
T2-T0 to think time statistics which just doesn't make any sence (the
queue's think time is penalized by the queue being able to submit more
IO). So add to think time statistics only time intervals when the queue
had no IO pending.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/bfq-iosched.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 19c59a69a4d5..bf16e8329a81 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5251,8 +5251,16 @@ static void bfq_update_io_thinktime(struct bfq_data *bfqd,
 				    struct bfq_queue *bfqq)
 {
 	struct bfq_ttime *ttime = &bfqq->ttime;
-	u64 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;
-
+	u64 elapsed;
+	
+	/*
+	 * We are really interested in how long it takes for the queue to
+	 * become busy when there is no outstanding IO for this queue. So
+	 * ignore cases when the bfq queue has already IO queued.
+	 */
+	if (bfqq->dispatched || bfq_bfqq_busy(bfqq))
+		return;
+	elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;
 	elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);
 
 	ttime->ttime_samples = (7*ttime->ttime_samples + 256) / 8;
-- 
2.16.4