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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no 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 D7727C3A589 for ; Wed, 21 Aug 2019 01:05:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B038B22D6D for ; Wed, 21 Aug 2019 01:05:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726441AbfHUBFC (ORCPT ); Tue, 20 Aug 2019 21:05:02 -0400 Received: from out30-45.freemail.mail.aliyun.com ([115.124.30.45]:35919 "EHLO out30-45.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726215AbfHUBFC (ORCPT ); Tue, 20 Aug 2019 21:05:02 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R481e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07486;MF=joseph.qi@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0Ta0LkxB_1566349497; Received: from JosephdeMacBook-Pro.local(mailfrom:joseph.qi@linux.alibaba.com fp:SMTPD_---0Ta0LkxB_1566349497) by smtp.aliyun-inc.com(127.0.0.1); Wed, 21 Aug 2019 09:04:57 +0800 Subject: Re: [RFC] performance regression with "ext4: Allow parallel DIO reads" To: "Theodore Y. Ts'o" Cc: Jan Kara , Joseph Qi , Dave Chinner , Andreas Dilger , Ext4 Developers List , Xiaoguang Wang , Liu Bo References: <29d50d24-f8e7-5ef4-d4d8-3ea6fb1c6ed3@gmail.com> <6DADA28C-542F-45F6-ADB0-870A81ABED23@dilger.ca> <15112e38-94fe-39d6-a8e2-064ff47187d5@linux.alibaba.com> <20190728225122.GG7777@dread.disaster.area> <960bb915-20cc-26a0-7abc-bfca01aa39c0@gmail.com> <20190815151336.GO14313@quack2.suse.cz> <075fd06f-b0b4-4122-81c6-e49200d5bd17@linux.alibaba.com> <20190816145719.GA3041@quack2.suse.cz> <20190820160805.GB10232@mit.edu> From: Joseph Qi Message-ID: Date: Wed, 21 Aug 2019 09:04:57 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190820160805.GB10232@mit.edu> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org Hi Ted， On 19/8/21 00:08, Theodore Y. Ts'o wrote: > On Tue, Aug 20, 2019 at 11:00:39AM +0800, Joseph Qi wrote: >> >> I've tested parallel dio reads with dioread_nolock, it doesn't have >> significant performance improvement and still poor compared with reverting >> parallel dio reads. IMO, this is because with parallel dio reads, it take >> inode shared lock at the very beginning in ext4_direct_IO_read(). > > Why is that a problem? It's a shared lock, so parallel threads should > be able to issue reads without getting serialized? > The above just tells the result that even mounting with dioread_nolock, parallel dio reads still has poor performance than before (w/o parallel dio reads). > Are you using sufficiently fast storage devices that you're worried > about cache line bouncing of the shared lock? Or do you have some > other concern, such as some other thread taking an exclusive lock? > The test case is random read/write described in my first mail. And from my preliminary investigation, shared lock consumes more in such scenario. Thanks, Joseph