From mboxrd@z Thu Jan 1 00:00:00 1970 From: Suresh Jayaraman Subject: Re: [LSF/MM TOPIC] [ATTEND] Throttling I/O Date: Mon, 28 Jan 2013 17:16:30 +0530 Message-ID: <51066516.4000501@suse.com> References: <51028666.1080109@suse.com> <20130125175711.GJ3081@htj.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, Fengguang Wu , Andrea Righi , Vivek Goyal , Jan Kara , Moyer Jeff Moyer To: Tejun Heo Return-path: Received: from cantor2.suse.de ([195.135.220.15]:56053 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754205Ab3A1Lqr (ORCPT ); Mon, 28 Jan 2013 06:46:47 -0500 In-Reply-To: <20130125175711.GJ3081@htj.dyndns.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On 01/25/2013 11:27 PM, Tejun Heo wrote: > Hey, Suresh. > > On Fri, Jan 25, 2013 at 06:49:34PM +0530, Suresh Jayaraman wrote: >> - Making cfq schedule the per cgroup sync/async queues according to I/O >> weights would mean that we'll need to use per cgroup cfqq's instead >> of per process? What will the impact on sync latencies if for example >> we have many sync only tasks in one cgroup and many async tasks in >> another? What if BLK_CGROUP is not configured, what would be the >> fallback behavior? > > So, we currently have synd cfqqs in cgroup cfqgs and shared cfqqs in > the root cfqg. The end result would be splitting shared cfqqs into > cgroup cfqgs. We may have to change how cfqgs are chosen depending on > whether it only has async IOs pending. Not sure. Ah, ok. Even if we have a way to check if in a particular cgroup all I/O is async or not, I have feeling that sync latencies might still get impacted for e.g. if we have a very few sync tasks plus many async tasks in one cgroup competing with all sync tasks in another group or some other combinations, no? Thanks -- Suresh Jayaraman