From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752181AbdJCOlP (ORCPT ); Tue, 3 Oct 2017 10:41:15 -0400 Received: from mail-it0-f44.google.com ([209.85.214.44]:50594 "EHLO mail-it0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751914AbdJCOlN (ORCPT ); Tue, 3 Oct 2017 10:41:13 -0400 X-Google-Smtp-Source: AOwi7QCdHIcGPEfKDoc3GwtTyZtk8/xCh8ST4WAPvIhANlNsp/33iy/2RdjwVv2OhKGexAuKRU0nQQ== Subject: Re: [PATCH BUGFIX/IMPROVEMENT 0/4] block, bfq: series of fixes of bugs affecting service guarantees To: Paolo Valente Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, broonie@kernel.org, lee.tibbert@gmail.com, oleksandr@natalenko.name, mirkomontanari91@gmail.com, angeloruocco90@gmail.com, mauro.andreolini@unimore.it References: <20170921090403.3217-1-paolo.valente@linaro.org> From: Jens Axboe Message-ID: Date: Tue, 3 Oct 2017 08:41:10 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20170921090403.3217-1-paolo.valente@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/21/2017 03:03 AM, Paolo Valente wrote: > Hi, > the first patch in this series fixes a bug that causes bfq to fail to > guarantee a high responsiveness on some drives, if there is heavy > random read+write I/O in the background. More precisely, such a > failure allowed this bug to be found [1], but the bug may well cause > other yet unreported anomalies. > > This fix uncovered other bugs that were concealed by the fixed bug, > for rather subtle reasons. These further bugs caused similar > responsiveness failures, but with sequential reaad+write workloads in > the background. The remaining three patches fix these further bugs. > > The sum of these fixes makes responsiveness much stabler with BFQ. In > the presence of write hogs, it is however still impossible for an I/O > scheduler to guarantee perfect responsiveness in any circustance, > because of throttling issues in the virtual-memory management > subsystem, and in other higher-level components. Added for 4.15, thanks. -- Jens Axboe