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From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
	Paolo Valente <paolo.valente@linaro.org>,
	linux-kernel@vger.kernel.org
Subject: [PATCH] block, bfq: keep peak_rate estimation within range 1..2^32-1
Date: Mon, 05 Mar 2018 15:48:53 +0300	[thread overview]
Message-ID: <152025413365.161046.7757556276366364549.stgit@buzz> (raw)

Rate should never overflow or become zero because it is used as divider.
This patch accumulates it with saturation.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
 block/bfq-iosched.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index aeca22d91101..a236c8d541b5 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2546,7 +2546,8 @@ static void bfq_reset_rate_computation(struct bfq_data *bfqd,
 
 static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
 {
-	u32 rate, weight, divisor;
+	u32 weight, divisor;
+	u64 rate;
 
 	/*
 	 * For the convergence property to hold (see comments on
@@ -2634,9 +2635,10 @@ static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
 	 */
 	bfqd->peak_rate *= divisor-1;
 	bfqd->peak_rate /= divisor;
-	rate /= divisor; /* smoothing constant alpha = 1/divisor */
+	do_div(rate, divisor);	/* smoothing constant alpha = 1/divisor */
 
-	bfqd->peak_rate += rate;
+	/* rate should never overlow or become zero */
+	bfqd->peak_rate = clamp_t(u64, rate + bfqd->peak_rate, 1, U32_MAX);
 	update_thr_responsiveness_params(bfqd);
 
 reset_computation:

             reply	other threads:[~2018-03-05 12:49 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-05 12:48 Konstantin Khlebnikov [this message]
2018-03-19  6:03 ` Paolo Valente
2018-03-19  6:28   ` Konstantin Khlebnikov
2018-03-20  3:00     ` Paolo Valente
2018-03-20  7:41       ` Konstantin Khlebnikov
2018-03-20 23:49         ` Paolo Valente
2018-03-26  8:01           ` Paolo Valente
2018-03-26 10:28             ` Konstantin Khlebnikov
2018-03-26 14:06               ` Paolo Valente
2018-03-26 14:18                 ` Konstantin Khlebnikov

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