From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7229CC64EB8 for ; Sat, 6 Oct 2018 03:12:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3259A213A2 for ; Sat, 6 Oct 2018 03:12:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3259A213A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=acm.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729425AbeJFKOI (ORCPT ); Sat, 6 Oct 2018 06:14:08 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:34453 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726919AbeJFKOH (ORCPT ); Sat, 6 Oct 2018 06:14:07 -0400 Received: by mail-pf1-f196.google.com with SMTP id k19-v6so5915837pfi.1; Fri, 05 Oct 2018 20:12:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=CrlANVbBXs5JGvkHTjl/dhpKTstM6Ljvh1WcfzwIkTk=; b=jPijW4ZLfQpngUp3ViwsD2Y8Fu+m4u6uxxGf9Mozv/l4kANqOO4zh2X4BS5iAfVAXE bK3oZYPAQYiT+1vwNDNloSq3+J4onG+jP5oIpkYExnURRM1IQsVt0JP5+xi6iYZRimwr pqROzU8uNxIh44Lvw/Nq+dVTkDUnJYHKOsLNkBGYcFyfF8cN3ojjrznGjJzzKGTOnbtu Zz2dcJK2JAe57cYzwfYYbnlmwhJ2h2TrYtgIpvD6THswwoOVxcNQ2Gw4HH524M1EGAw5 u6gM0RR3w9085BaXYKnulmkF7IC5VO7tW84h/l6lS0K0rOoJ5mOqUjmUc1RexDWMWBwO K/Ng== X-Gm-Message-State: ABuFfogY+OFUiP+iRIPol/ACNs9grHPbuUnBj9n4vtY+3mF6592NyLM9 Zaab4+l5tjqo/p2XzqcusFgupEHWH5EkPQ== X-Google-Smtp-Source: ACcGV60vt0thEFT/IFJdCdaI1179ELHPkMVl8AHFxlKNeTArKWZHrDZwIYs5MgfQNWZDFZ+k+uyGHw== X-Received: by 2002:a63:4107:: with SMTP id o7-v6mr12673225pga.256.1538795550196; Fri, 05 Oct 2018 20:12:30 -0700 (PDT) Received: from asus.site ([2601:647:4601:42b4:3842:3e31:3bb6:cf62]) by smtp.gmail.com with ESMTPSA id 84-v6sm20127910pfs.108.2018.10.05.20.12.28 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 05 Oct 2018 20:12:29 -0700 (PDT) Subject: Re: [PATCH] block: BFQ default for single queue devices To: Jan Kara Cc: Paolo Valente , 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 , Andreas Herrmann , Mel Gorman , Chunyan Zhang , linux-kernel 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> <1538692972.8223.7.camel@acm.org> <20181005091626.GA9686@quack2.suse.cz> From: Bart Van Assche Message-ID: <20bfa679-3131-e0af-f69d-2fbec32fbced@acm.org> Date: Fri, 5 Oct 2018 20:12:27 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <20181005091626.GA9686@quack2.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/5/18 2:16 AM, Jan Kara wrote: > On Thu 04-10-18 15:42:52, Bart Van Assche wrote: >> 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->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. > > Well, I'm not sure why that is missing. I don't think anyone proposed to > default to BFQ for such setup? Neither was anyone claiming that BFQ is > better in such situation... The proposal has been: Default to BFQ for slow > storage, leave it to deadline-mq otherwise. Hi Jan, How do you define slow storage? The proposal at the start of this thread was to make BFQ the default for all block devices that create a single hardware queue. That includes all SATA storage since scsi-mq only creates a single hardware queue when using the SATA protocol. The proposal to make BFQ the default for systems with a single hard disk probably makes sense but I am not sure that making BFQ the default for systems equipped with one or more (SATA) SSDs is also a good idea. Especially for multi-socket systems since BFQ reintroduces a queue-wide lock. As you know no queue-wide locking happens during I/O in the scsi-mq core nor in the blk-mq core. Bart.