From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761426Ab3EBTAA (ORCPT ); Thu, 2 May 2013 15:00:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:7798 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761292Ab3EBS77 (ORCPT ); Thu, 2 May 2013 14:59:59 -0400 Date: Thu, 2 May 2013 14:59:52 -0400 From: Vivek Goyal To: Tejun Heo Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, lizefan@huawei.com, containers@lists.linux-foundation.org, cgroups@vger.kernel.org Subject: Re: [PATCHSET] blk-throttle: implement proper hierarchy support Message-ID: <20130502185952.GJ30020@redhat.com> References: <1367455189-6957-1-git-send-email-tj@kernel.org> <20130502173428.GA4771@redhat.com> <20130502180815.GG30020@redhat.com> <20130502184426.GO19814@mtj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130502184426.GO19814@mtj.dyndns.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 02, 2013 at 11:44:26AM -0700, Tejun Heo wrote: [..] > Also, if you're actually thinking about reimplementing blk-throttle, > please do consider the followings. > > * Currently, blk-throttle doesn't throttle the number of bios being > queued. Note that this breaks the basic back-pressure mechanism > where IO pressure is propagated back to the issuer by throttling the > issuing task. blk-throttle breaks that link and converts it to a > memory pressure. Agreed. Implementing something along the lines of per group nr_requests is needed. > > * It's almost inherently unscalable with highops devices. Given that > IO limiting doesn't require very fine granularity, I think doing > this per-cpu shouldn't be too hard. e.g. build a per-cpu token > distributing hierarchy with rebalancing across CPUs happening > periodically. Interesting. I thought for highops devices we will these multi queue patches from jens and there we can probably implement per queue tokens and rebalance tokens across queues periodically. > > In short, right now, the goal is getting the hierarchy support > acceptably working ASAP and yeap we wanna get the nested limits and at > least certain level of fairness, but let's please implement something > simple for now and strive for sophistification later because it's > holding back everyone else. I am fine with this. Having some hierarchical algorithm and not blocking full hierarchical support for cgroup is better than not having any hierachical support and wait for better implementation. Thanks Vivek