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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 3D0D6C4CEC9 for ; Tue, 17 Sep 2019 21:32:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0EB83214AF for ; Tue, 17 Sep 2019 21:32:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568755935; bh=TLP3vC8rXSnAqiAPCukYCogpSW8wtn0P2LZHI1QIO60=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=iKwrnEI4zIePJDdrNEJvrV6KWaH5po25Z+wu07g1bpvytSnmLhejBqtG/3osgU3fV yFx7TQUnW9qCLHrAUyFsU73tPgXmdnJ1sjd1b3S79mq7l1QomIW7GEobIB0WIZPR64 dczftFOjp5GVUuUOYJRhEnhpiZH0zlaep91/gnbk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728392AbfIQVcO (ORCPT ); Tue, 17 Sep 2019 17:32:14 -0400 Received: from mail-qk1-f196.google.com ([209.85.222.196]:40439 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726369AbfIQVcO (ORCPT ); Tue, 17 Sep 2019 17:32:14 -0400 Received: by mail-qk1-f196.google.com with SMTP id y144so5677426qkb.7; Tue, 17 Sep 2019 14:32:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=6cdjH5M5cwq0sm332RdYEPiqfQpF2RR9LsPCpbZYDwQ=; b=IHkrkyrTjqmtC97bG84hTy/5TfojbkwbxNX5Z7uREwvPtxFj/px0ZiyGIn1bJjByWB x1ecC8HiuApwY5CvSfB5gDPN1az2OY0iUc+/6d+lY4u9HW0lsKcyNz76olwUJAJIVs0Y 3Li8WS9rLHfQw63VdijGqDhnEJvHg1itxFegJr0FsZKXldWyRaQ7tfcQVazjYi8byce4 WsIBOadrzh6E2Rsbv7/KqvUghALMKnW6guJ4npItSpsJzUl2Vuo1XMssafXzY4ztboOV ejrg9wzd8b8zOYNZ1whxd+fhPIRYd7sO35Xlysx6IyF06TVbkLIWFYfZ4y7lY75KI+t3 oFUQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=6cdjH5M5cwq0sm332RdYEPiqfQpF2RR9LsPCpbZYDwQ=; b=Ef+K58H3toXKYWg6c51cpMmsig+qfMe5XoIvXckjvBVqj1HflWY8ea3KFvfow52vPT xgCOJ1u7YXb6KvB7WrKZFVs4frQmgYJlGLeo5rnm5TlvfMZee8MHnoiPW+nGwL3q/HYI N/smtwnTmoYsfe0aREGmrDy0NJecDbLnuc5y4VKH0nx5x5q0+irENQ6lGTUJAlSWPCaP 186mO1ewvgVpgdZMq2yZo26gxRf1iTONlB/RuMmvMAeXcjGyuXLMcIbK9PSTo2/jfOTk S/PKSPCEHQQ+P0Qaj/aJ4otGwsSeWRzuYm9UeV1BcGACbV1OncL7V0meXa9sBOjzKtkQ YIhg== X-Gm-Message-State: APjAAAWB9dh+iaDgq0/XUGYYJdtc+IgR0R+kfptACTcZIgiqNbPNACDm xSB1e3Iva16l/nFjt8TruQw= X-Google-Smtp-Source: APXvYqycwixHNwFOx7BoUh+it495gVkAadq75SnqbuisTQER8fPpW0/0pdgi3fY2R20GFUsedQZH+w== X-Received: by 2002:a37:6358:: with SMTP id x85mr655232qkb.229.1568755932462; Tue, 17 Sep 2019 14:32:12 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::642e]) by smtp.gmail.com with ESMTPSA id o8sm1744194qte.47.2019.09.17.14.32.11 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 17 Sep 2019 14:32:11 -0700 (PDT) Date: Tue, 17 Sep 2019 14:32:09 -0700 From: Tejun Heo To: Paolo Valente Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, linus.walleij@linaro.org, bfq-iosched@googlegroups.com, oleksandr@natalenko.name, cgroups@vger.kernel.org, Angelo Ruocco Subject: Re: [PATCH 2/2] block, bfq: delete "bfq" prefix from cgroup filenames Message-ID: <20190917213209.GK3084169@devbig004.ftw2.facebook.com> References: <20190917165148.19146-1-paolo.valente@linaro.org> <20190917165148.19146-3-paolo.valente@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190917165148.19146-3-paolo.valente@linaro.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Tue, Sep 17, 2019 at 06:51:48PM +0200, Paolo Valente wrote: > When bfq was merged into mainline, there were two I/O schedulers that > implemented the proportional-share policy: bfq for blk-mq and cfq for > legacy blk. bfq's interface files in the blkio/io controller have the > same names as cfq. But the cgroups interface doesn't allow two > entities to use the same name for their files, so for bfq we had to > prepend the "bfq" prefix to each of its files. However no legacy code > uses these modified file names. This naming also causes confusion, as, > e.g., in [1]. > > Now cfq has gone with legacy blk, so there is no need any longer for > these prefixes in (the never used) bfq names. In view of this fact, this > commit removes these prefixes, thereby enabling legacy code to truly > use the proportional share policy in blk-mq. So, I wrote the iocost switching patch and don't have a strong interest in whether bfq prefix should get dropped or not. However, I gotta point out that flipping interface this way is way out of the norm. In the previous release cycle, the right thing to do was dropping the bfq prefix but that wasn't possible because bfq's interface wasn't compatible at that point and didn't made to be compatible in time. Non-obviously different interface with the same name is a lot worse than giving it a new name, so the only acceptable course of action at that point was keeping the bfq prefix. Now that the interface has already been published in a released kernel, dropping the prefix would be something extremely unusual as there would already be users who will be affected by the interface flip-flop. We sometimes do change interfaces but I'm having a difficult time seeing the overriding rationales in this case. Thanks. -- tejun