From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753200Ab2AWPjT (ORCPT ); Mon, 23 Jan 2012 10:39:19 -0500 Received: from mail-gx0-f174.google.com ([209.85.161.174]:40279 "EHLO mail-gx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752122Ab2AWPjS (ORCPT ); Mon, 23 Jan 2012 10:39:18 -0500 Date: Mon, 23 Jan 2012 07:39:13 -0800 From: Tejun Heo To: Vivek Goyal Cc: axboe@kernel.dk, ctalbott@google.com, rni@google.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 08/17] blkcg: shoot down blkio_groups on elevator switch Message-ID: <20120123153913.GB12652@google.com> References: <1327202725-3383-1-git-send-email-tj@kernel.org> <1327202725-3383-9-git-send-email-tj@kernel.org> <20120123152055.GD25986@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120123152055.GD25986@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Mon, Jan 23, 2012 at 10:20:55AM -0500, Vivek Goyal wrote: > What happens to per device rules (per device weight and per device > throttling rules)? IIUC, in new scheme of things, upon elevator switch > these rules will be gone. > > I can understand per device weight rules disappearing but what about > throttling rules. They are independent of IO scheduler and change of > io scheduler should not cause per device throttling rules to get lost. > > This just gets worse if elevator switch fails and we fall back to old > elevator. But now we have lost of the rules as rules were part of > blkg.conf and old groups are gone. As any other choices, it's about trade off and there multiple aspects to consider. Both elevator and policy changes are extremely low frequency and inherently disruptive operations and having persistency across them doesn't justify adding the amount of complexity and design convolutions we have now, especially not when rule persistency across those switches can be implemented with mostly trivial switching script from userland. Thanks. -- tejun