From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Subject: Re: [PATCH RFC 10/22] block, bfq: add full hierarchical scheduling and cgroups support Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: text/plain; charset=windows-1252 From: Paolo Valente In-Reply-To: <20160422181321.GV7822@mtj.duckdns.org> Date: Fri, 22 Apr 2016 20:19:47 +0200 Cc: Jens Axboe , Fabio Checconi , Arianna Avanzini , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, linus.walleij@linaro.org, broonie@kernel.org Message-Id: References: <1454364778-25179-1-git-send-email-paolo.valente@linaro.org> <1454364778-25179-11-git-send-email-paolo.valente@linaro.org> <20160211222824.GD3741@mtj.duckdns.org> <57174CA7.5000706@linaro.org> <20160422181321.GV7822@mtj.duckdns.org> To: Tejun Heo List-ID: Il giorno 22/apr/2016, alle ore 20:13, Tejun Heo ha = scritto: > Hello, Paolo. >=20 > On Wed, Apr 20, 2016 at 11:32:23AM +0200, Paolo wrote: >> This malfunction seems related to a blkcg behavior that I did not >> expect: the sequential writer changes group continuously. It moves >> from the root group to its correct group, and back. Here is the >> output of >>=20 >> egrep 'insert_request|changed cgroup' trace >>=20 >> over a trace taken with the original version of cfq (seq_write is of >> course the group of the writer): > ... >> For reasons that I don't yet know, group changes are much more >> frequent with bfq, which ultimately causes bfq to fail to isolate the >> writer from the reader. >>=20 >> While I go on trying to understand why, could you please tell me >> whether this fluctuation is normal, and/or point me to documentation = from >> which I can better understand this behavior, without bothering you >> further? >=20 > So, a kworker would jump through different workqueues and issue IOs > for different writeback domains and the context can't be tied to the > issuing task. The cgroup membership should be determined directly > from the bio. Yes. My doubt arises from the fact that the only source of intense I/O is the dd (I have executed it alone). In contrast, group changes occur at a high frequency during all the execution of the dd. Apparently I cannot see any other I/O induced by the dd. Journaling issues sync requests. > cfq uses per-cgroup async queue. I'm not sure how this > would map to bfq tho. >=20 It=92s the same. But this is the part I=92m checking. Thanks, Paolo > Thanks. >=20 > --=20 > tejun From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752962AbcDVSTz (ORCPT ); Fri, 22 Apr 2016 14:19:55 -0400 Received: from mail-wm0-f42.google.com ([74.125.82.42]:38798 "EHLO mail-wm0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752164AbcDVSTy convert rfc822-to-8bit (ORCPT ); Fri, 22 Apr 2016 14:19:54 -0400 Subject: Re: [PATCH RFC 10/22] block, bfq: add full hierarchical scheduling and cgroups support Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: text/plain; charset=windows-1252 From: Paolo Valente In-Reply-To: <20160422181321.GV7822@mtj.duckdns.org> Date: Fri, 22 Apr 2016 20:19:47 +0200 Cc: Jens Axboe , Fabio Checconi , Arianna Avanzini , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, linus.walleij@linaro.org, broonie@kernel.org Content-Transfer-Encoding: 8BIT Message-Id: References: <1454364778-25179-1-git-send-email-paolo.valente@linaro.org> <1454364778-25179-11-git-send-email-paolo.valente@linaro.org> <20160211222824.GD3741@mtj.duckdns.org> <57174CA7.5000706@linaro.org> <20160422181321.GV7822@mtj.duckdns.org> To: Tejun Heo X-Mailer: Apple Mail (2.1878.6) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Il giorno 22/apr/2016, alle ore 20:13, Tejun Heo ha scritto: > Hello, Paolo. > > On Wed, Apr 20, 2016 at 11:32:23AM +0200, Paolo wrote: >> This malfunction seems related to a blkcg behavior that I did not >> expect: the sequential writer changes group continuously. It moves >> from the root group to its correct group, and back. Here is the >> output of >> >> egrep 'insert_request|changed cgroup' trace >> >> over a trace taken with the original version of cfq (seq_write is of >> course the group of the writer): > ... >> For reasons that I don't yet know, group changes are much more >> frequent with bfq, which ultimately causes bfq to fail to isolate the >> writer from the reader. >> >> While I go on trying to understand why, could you please tell me >> whether this fluctuation is normal, and/or point me to documentation from >> which I can better understand this behavior, without bothering you >> further? > > So, a kworker would jump through different workqueues and issue IOs > for different writeback domains and the context can't be tied to the > issuing task. The cgroup membership should be determined directly > from the bio. Yes. My doubt arises from the fact that the only source of intense I/O is the dd (I have executed it alone). In contrast, group changes occur at a high frequency during all the execution of the dd. Apparently I cannot see any other I/O induced by the dd. Journaling issues sync requests. > cfq uses per-cgroup async queue. I'm not sure how this > would map to bfq tho. > It’s the same. But this is the part I’m checking. Thanks, Paolo > Thanks. > > -- > tejun