From patchwork Mon Aug 8 11:15:11 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Valente X-Patchwork-Id: 73443 Delivered-To: patch@linaro.org Received: by 10.140.29.52 with SMTP id a49csp3160499qga; Mon, 8 Aug 2016 04:18:51 -0700 (PDT) X-Received: by 10.98.90.133 with SMTP id o127mr161140775pfb.61.1470655130447; Mon, 08 Aug 2016 04:18:50 -0700 (PDT) Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id m5si9186587pai.102.2016.08.08.04.18.50; Mon, 08 Aug 2016 04:18:50 -0700 (PDT) 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; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE dis=NONE) header.from=linaro.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752726AbcHHLSm (ORCPT + 27 others); Mon, 8 Aug 2016 07:18:42 -0400 Received: from smtp26.sms.unimo.it ([155.185.44.26]:60142 "EHLO smtp26.sms.unimo.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752420AbcHHLSc (ORCPT ); Mon, 8 Aug 2016 07:18:32 -0400 Received: from [185.14.9.10] (port=55814 helo=localhost.localdomain) by smtp26.sms.unimo.it with esmtpsa (TLS1.2:RSA_AES_128_CBC_SHA256:128) (Exim 4.80) (envelope-from ) id 1bWiXv-00051g-TU; Mon, 08 Aug 2016 13:16:40 +0200 From: Paolo Valente To: Jens Axboe , Tejun Heo Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, linus.walleij@linaro.org, broonie@kernel.org, Paolo Valente , Arianna Avanzini Subject: [PATCH V2 16/22] block, bfq: preserve a low latency also with NCQ-capable drives Date: Mon, 8 Aug 2016 13:15:11 +0200 Message-Id: <1470654917-4280-17-git-send-email-paolo.valente@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1470654917-4280-1-git-send-email-paolo.valente@linaro.org> References: <1470654917-4280-1-git-send-email-paolo.valente@linaro.org> UNIMORE-X-SA-Score: -2.9 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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(-) -- 1.9.1 diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 932adfd..d3cda1a 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -5524,7 +5524,8 @@ 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 &&