From patchwork Wed Jul 27 16:13:32 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Valente X-Patchwork-Id: 9250117 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id C32EE60B18 for ; Wed, 27 Jul 2016 16:18:01 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B4B0D26598 for ; Wed, 27 Jul 2016 16:18:01 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id A995527D5D; Wed, 27 Jul 2016 16:18:01 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 7374426D06 for ; Wed, 27 Jul 2016 16:17:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757659AbcG0QRh (ORCPT ); Wed, 27 Jul 2016 12:17:37 -0400 Received: from spostino.sms.unimo.it ([155.185.44.3]:53073 "EHLO spostino.sms.unimo.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757634AbcG0QRg (ORCPT ); Wed, 27 Jul 2016 12:17:36 -0400 Received: from [185.14.9.64] (port=43484 helo=localhost.localdomain) by spostino.sms.unimo.it with esmtpsa (TLS1.2:RSA_AES_128_CBC_SHA256:128) (Exim 4.80) (envelope-from ) id 1bSRUJ-0005Yz-Jz; Wed, 27 Jul 2016 18:15:16 +0200 From: Paolo Valente To: Jens Axboe , Tejun Heo Cc: Fabio Checconi , Arianna Avanzini , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, linus.walleij@linaro.org, broonie@kernel.org, Paolo Valente Subject: [PATCH RFC V8 16/22] block, bfq: preserve a low latency also with NCQ-capable drives Date: Wed, 27 Jul 2016 18:13:32 +0200 Message-Id: <1469636018-31247-17-git-send-email-paolo.valente@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1469636018-31247-1-git-send-email-paolo.valente@linaro.org> References: <2D83ACA0-2513-4019-9A0D-3166FDDE7485@linaro.org> <1469636018-31247-1-git-send-email-paolo.valente@linaro.org> UNIMORE-X-SA-Score: -2.9 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP I/O schedulers typically allow NCQ-capable drives to prefetch I/O requests, as NCQ boosts the throughput exactly by prefetching and internally reordering requests. Unfortunately, as discussed in detail and shown experimentally in [1], this may cause fairness and latency guarantees to be violated. The main problem is that the internal scheduler of an NCQ-capable drive may postpone the service of some unlucky (prefetched) requests as long as it deems serving other requests more appropriate to boost the throughput. This patch addresses this issue by not disabling device idling for weight-raised queues, even if the device supports NCQ. This allows BFQ to start serving a new queue, and therefore allows the drive to prefetch new requests, only after the idling timeout expires. At that time, all the outstanding requests of the expired queue have been most certainly served. [1] P. Valente and M. Andreolini, "Improving Application Responsiveness with the BFQ Disk I/O Scheduler", Proceedings of the 5th Annual International Systems and Storage Conference (SYSTOR '12), June 2012. Slightly extended version: http://algogroup.unimore.it/people/paolo/disk_sched/bfq-v1-suite- results.pdf Signed-off-by: Paolo Valente Signed-off-by: Arianna Avanzini --- block/cfq-iosched.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index bdf97bc..5207ed8 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -5490,7 +5490,8 @@ static void bfq_update_idle_window(struct bfq_data *bfqd, if (atomic_read(&bic->icq.ioc->active_ref) == 0 || bfqd->bfq_slice_idle == 0 || - (bfqd->hw_tag && BFQQ_SEEKY(bfqq))) + (bfqd->hw_tag && BFQQ_SEEKY(bfqq) && + bfqq->wr_coeff == 1)) enable_idle = 0; else if (bfq_sample_valid(bic->ttime.ttime_samples)) { if (bic->ttime.ttime_mean > bfqd->bfq_slice_idle &&