From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934970AbeCEMtC (ORCPT ); Mon, 5 Mar 2018 07:49:02 -0500 Received: from forwardcorp1o.cmail.yandex.net ([37.9.109.47]:39702 "EHLO forwardcorp1o.cmail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934877AbeCEMs7 (ORCPT ); Mon, 5 Mar 2018 07:48:59 -0500 Authentication-Results: smtpcorp1o.mail.yandex.net; dkim=pass header.i=@yandex-team.ru Subject: [PATCH] block, bfq: keep peak_rate estimation within range 1..2^32-1 From: Konstantin Khlebnikov To: linux-block@vger.kernel.org, Jens Axboe , Paolo Valente , linux-kernel@vger.kernel.org Date: Mon, 05 Mar 2018 15:48:53 +0300 Message-ID: <152025413365.161046.7757556276366364549.stgit@buzz> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Rate should never overflow or become zero because it is used as divider. This patch accumulates it with saturation. Signed-off-by: Konstantin Khlebnikov --- 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: