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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 86E9AC04AAF for ; Tue, 21 May 2019 07:19:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6366D2173C for ; Tue, 21 May 2019 07:19:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726242AbfEUHTq (ORCPT ); Tue, 21 May 2019 03:19:46 -0400 Received: from outgoing-stata.csail.mit.edu ([128.30.2.210]:57311 "EHLO outgoing-stata.csail.mit.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725809AbfEUHTq (ORCPT ); Tue, 21 May 2019 03:19:46 -0400 Received: from c-73-193-85-113.hsd1.wa.comcast.net ([73.193.85.113] helo=srivatsab-a01.vmware.com) by outgoing-stata.csail.mit.edu with esmtpsa (TLS1.2:RSA_AES_128_CBC_SHA1:128) (Exim 4.82) (envelope-from ) id 1hSz3h-000Bpw-PS; Tue, 21 May 2019 03:19:37 -0400 Subject: Re: CFQ idling kills I/O performance on ext4 with blkio cgroup controller To: Paolo Valente Cc: linux-fsdevel@vger.kernel.org, linux-block , linux-ext4@vger.kernel.org, cgroups@vger.kernel.org, kernel list , Jens Axboe , Jan Kara , jmoyer@redhat.com, Theodore Ts'o , amakhalov@vmware.com, anishs@vmware.com, srivatsab@vmware.com References: <8d72fcf7-bbb4-2965-1a06-e9fc177a8938@csail.mit.edu> <1812E450-14EF-4D5A-8F31-668499E13652@linaro.org> <46c6a4be-f567-3621-2e16-0e341762b828@csail.mit.edu> <07D11833-8285-49C2-943D-E4C1D23E8859@linaro.org> <238e14ff-68d1-3b21-a291-28de4f2d77af@csail.mit.edu> <6EB6C9D2-E774-48FA-AC95-BC98D97645D0@linaro.org> From: "Srivatsa S. Bhat" Message-ID: Date: Tue, 21 May 2019 00:19:29 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <6EB6C9D2-E774-48FA-AC95-BC98D97645D0@linaro.org> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 5/20/19 11:23 PM, Paolo Valente wrote: > > >> Il giorno 21 mag 2019, alle ore 00:45, Srivatsa S. Bhat ha scritto: >> >> On 5/20/19 3:19 AM, Paolo Valente wrote: >>> >>> >>>> Il giorno 18 mag 2019, alle ore 22:50, Srivatsa S. Bhat ha scritto: >>>> >>>> On 5/18/19 11:39 AM, Paolo Valente wrote: >>>>> I've addressed these issues in my last batch of improvements for BFQ, >>>>> which landed in the upcoming 5.2. If you give it a try, and still see >>>>> the problem, then I'll be glad to reproduce it, and hopefully fix it >>>>> for you. >>>>> >>>> >>>> Hi Paolo, >>>> >>>> Thank you for looking into this! >>>> >>>> I just tried current mainline at commit 72cf0b07, but unfortunately >>>> didn't see any improvement: >>>> >>>> dd if=/dev/zero of=/root/test.img bs=512 count=10000 oflag=dsync >>>> >>>> With mq-deadline, I get: >>>> >>>> 5120000 bytes (5.1 MB, 4.9 MiB) copied, 3.90981 s, 1.3 MB/s >>>> >>>> With bfq, I get: >>>> 5120000 bytes (5.1 MB, 4.9 MiB) copied, 84.8216 s, 60.4 kB/s >>>> >>> >>> Hi Srivatsa, >>> thanks for reproducing this on mainline. I seem to have reproduced a >>> bonsai-tree version of this issue. Before digging into the block >>> trace, I'd like to ask you for some feedback. >>> >>> First, in my test, the total throughput of the disk happens to be >>> about 20 times as high as that enjoyed by dd, regardless of the I/O >>> scheduler. I guess this massive overhead is normal with dsync, but >>> I'd like know whether it is about the same on your side. This will >>> help me understand whether I'll actually be analyzing about the same >>> problem as yours. >>> >> >> Do you mean to say the throughput obtained by dd'ing directly to the >> block device (bypassing the filesystem)? > > No no, I mean simply what follows. > > 1) in one terminal: > [root@localhost tmp]# dd if=/dev/zero of=/root/test.img bs=512 count=10000 oflag=dsync > 10000+0 record dentro > 10000+0 record fuori > 5120000 bytes (5,1 MB, 4,9 MiB) copied, 14,6892 s, 349 kB/s > > 2) In a second terminal, while the dd is in progress in the first > terminal: > $ iostat -tmd /dev/sda 3 > Linux 5.1.0+ (localhost.localdomain) 20/05/2019 _x86_64_ (2 CPU) > > ... > 20/05/2019 11:40:17 > Device tps MB_read/s MB_wrtn/s MB_read MB_wrtn > sda 2288,00 0,00 9,77 0 29 > > 20/05/2019 11:40:20 > Device tps MB_read/s MB_wrtn/s MB_read MB_wrtn > sda 2325,33 0,00 9,93 0 29 > > 20/05/2019 11:40:23 > Device tps MB_read/s MB_wrtn/s MB_read MB_wrtn > sda 2351,33 0,00 10,05 0 30 > ... > > As you can see, the overall throughput (~10 MB/s) is more than 20 > times as high as the dd throughput (~350 KB/s). But the dd is the > only source of I/O. > > Do you also see such a huge difference? > Ah, I see what you mean. Yes, I get a huge difference as well: I/O scheduler dd throughput Total throughput (via iostat) ------------- ------------- ----------------------------- mq-deadline or 1.6 MB/s 50 MB/s (30x) kyber bfq 60 KB/s 1 MB/s (16x) Regards, Srivatsa VMware Photon OS