Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Paolo Valente <paolo.valente@linaro.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        ulf.hansson@linaro.org, linus.walleij@linaro.org,
        bfq-iosched@googlegroups.com, oleksandr@natalenko.name,
        Paolo Valente <paolo.valente@linaro.org>
Subject: [PATCH 2/4] block, bfq: reduce upper bound for inject limit to max_rq_in_driver+1
Date:   Thu, 22 Aug 2019 17:20:35 +0200
Message-Id: <20190822152037.15413-3-paolo.valente@linaro.org>
In-Reply-To: <20190822152037.15413-1-paolo.valente@linaro.org>
References: <20190822152037.15413-1-paolo.valente@linaro.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Upon an increment attempt of the injection limit, the latter is
constrained not to become higher than twice the maximum number
max_rq_in_driver of I/O requests that have happened to be in service
in the drive. This high bound allows the injection limit to grow
beyond max_rq_in_driver, which may then cause max_rq_in_driver itself
to grow.

However, since the limit is incremented by only one unit at a time,
there is no need for such a high bound, and just max_rq_in_driver+1 is
enough.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
---
 block/bfq-iosched.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 5a2bbd8613a8..e114282204f6 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5805,7 +5805,7 @@ static void bfq_update_inject_limit(struct bfq_data *bfqd,
 			bfqq->inject_limit--;
 			bfqq->decrease_time_jif = jiffies;
 		} else if (tot_time_ns < threshold &&
-			   old_limit < bfqd->max_rq_in_driver<<1)
+			   old_limit <= bfqd->max_rq_in_driver)
 			bfqq->inject_limit++;
 	}
 
-- 
2.20.1