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([2620:15c:2cd:203:5cdc:422c:7b28:ebb5]) by smtp.gmail.com with ESMTPSA id f22-v6sm9226791pff.29.2018.10.04.15.42.53 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 04 Oct 2018 15:42:54 -0700 (PDT) Message-ID: <1538692972.8223.7.camel@acm.org> Subject: Re: [PATCH] block: BFQ default for single queue devices From: Bart Van Assche To: Paolo Valente Cc: Alan Cox , Jens Axboe , Linus Walleij , linux-block , linux-mmc , linux-mtd@lists.infradead.org, Pavel Machek , Ulf Hansson , Richard Weinberger , Artem Bityutskiy , Adrian Hunter , Jan Kara , Andreas Herrmann , Mel Gorman , Chunyan Zhang , linux-kernel Date: Thu, 04 Oct 2018 15:42:52 -0700 In-Reply-To: References: <20181002124329.21248-1-linus.walleij@linaro.org> <05fdbe23-ec01-895f-e67e-abff85c1ece2@kernel.dk> <1538582091.205649.20.camel@acm.org> <20181004202553.71c2599c@alans-desktop> <1538683746.230807.9.camel@acm.org> Content-Type: text/plain; charset="UTF-7" X-Mailer: Evolution 3.26.2-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2018-10-04 at 22:39 +-0200, Paolo Valente wrote: +AD4 No, kernel build is, for evident reasons, one of the workloads I cared +AD4 most about. Actually, I tried to focus on all my main +AD4 kernel-development tasks, such as also git checkout, git merge, git +AD4 grep, ... +AD4 +AD4 According to my test results, with BFQ these tasks are at least as +AD4 fast as, or, in most system configurations, much faster than with the +AD4 other schedulers. Of course, at the same time the system also remains +AD4 responsive with BFQ. +AD4 +AD4 You can repeat these tests using one of my first scripts in the S +AD4 suite: kern+AF8-dev+AF8-tasks+AF8-vs+AF8-rw.sh (usually, the older the tests, the more +AD4 hypertrophied the names I gave :) ). +AD4 +AD4 I stopped sharing also my kernel-build results years ago, because I +AD4 went on obtaining the same, identical good results for years, and I'm +AD4 aware that I tend to show and say too much stuff. On my test setup building the kernel is slightly slower when using the BFQ scheduler compared to using scheduler +ACI-none+ACI (kernel 4.18.12, NVMe SSD, single CPU with 6 cores, hyperthreading disabled). I am aware that the proposal at the start of this thread was to make BFQ the default for devices with a single hardware queue and not for devices like NVMe SSDs that support multiple hardware queues. What I think is missing is measurement results for BFQ on a system with multiple CPU sockets and against a fast storage medium. Eliminating the host lock from the SCSI core yielded a significant performance improvement for such storage devices. Since the BFQ scheduler locks and unlocks bfqd-+AD4-lock for every dispatch operation it is very likely that BFQ will slow down I/O for fast storage devices, even if their driver only creates a single hardware queue. Bart.