From patchwork Fri Apr 8 07:39:08 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yu Kuai X-Patchwork-Id: 12806197 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C3125C433EF for ; Fri, 8 Apr 2022 07:24:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229461AbiDHH0n (ORCPT ); Fri, 8 Apr 2022 03:26:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54184 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229469AbiDHH0m (ORCPT ); Fri, 8 Apr 2022 03:26:42 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7BBCA36939A; Fri, 8 Apr 2022 00:24:39 -0700 (PDT) Received: from kwepemi100010.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4KZV8C6FLFzgYXl; Fri, 8 Apr 2022 15:22:51 +0800 (CST) Received: from kwepemm600009.china.huawei.com (7.193.23.164) by kwepemi100010.china.huawei.com (7.221.188.54) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Fri, 8 Apr 2022 15:24:37 +0800 Received: from huawei.com (10.175.127.227) by kwepemm600009.china.huawei.com (7.193.23.164) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Fri, 8 Apr 2022 15:24:36 +0800 From: Yu Kuai To: , , , , CC: , , Subject: [PATCH -next RFC v2 0/8] improve tag allocation under heavy load Date: Fri, 8 Apr 2022 15:39:08 +0800 Message-ID: <20220408073916.1428590-1-yukuai3@huawei.com> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 X-Originating-IP: [10.175.127.227] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To kwepemm600009.china.huawei.com (7.193.23.164) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Changes in v2: - use a new title - add patches to fix waitqueues' unfairness - path 1-3 - delete patch to add queue flag - delete patch to split big io thoroughly There is a defect for blk-mq compare to blk-sq, specifically split io will end up discontinuous if the device is under high io pressure, while split io will still be continuous in sq, this is because: 1) new io can preempt tag even if there are lots of threads waiting. 2) split bio is issued one by one, if one bio can't get tag, it will go to wail. 3) each time 8(or wake batch) requests is done, 8 waiters will be woken up. Thus if a thread is woken up, it will unlikey to get multiple tags. The problem was first found by upgrading kernel from v3.10 to v4.18, test device is HDD with 256 'max_sectors_kb', and test case is issuing 1m ios with high concurrency. Noted that there is a precondition for such performance problem: There is a certain gap between bandwith for single io with bs=max_sectors_kb and disk upper limit. During the test, I found that waitqueues can be extremly unbalanced on heavy load. This is because 'wake_index' is not set properly in __sbq_wake_up(), see details in patch 3. In this patchset: - patch 1-3 fix waitqueues' unfairness. - patch 4,5 disable tag preemption on heavy load. - patch 6 forces tag preemption for split bios. - patch 7,8 improve large random io for HDD. As I mentioned above, we do meet the problem and I'm trying to fix it at very low cost. However, if anyone still thinks this is not a common case and not worth to optimize, I'll drop them. Test environment: arm64, 96 core with 200 BogoMIPS, test device is HDD. The default 'max_sectors_kb' is 1280(Sorry that I was unable to test on the machine where 'max_sectors_kb' is 256). The single io performance(randwrite): | bs | 128k | 256k | 512k | 1m | 1280k | 2m | 4m | | -------- | ---- | ---- | ---- | ---- | ----- | ---- | ---- | | bw MiB/s | 20.1 | 33.4 | 51.8 | 67.1 | 74.7 | 82.9 | 82.9 | It can be seen that 1280k io is already close to upper limit, and it'll be hard to see differences with the default value, thus I set 'max_sectors_kb' to 128 in the following test. Test cmd: fio \ -filename=/dev/$dev \ -name=test \ -ioengine=psync \ -allow_mounted_write=0 \ -group_reporting \ -direct=1 \ -offset_increment=1g \ -rw=randwrite \ -bs=1024k \ -numjobs={1,2,4,8,16,32,64,128,256,512} \ -runtime=110 \ -ramp_time=10 Test result: MiB/s | numjobs | v5.18-rc1 | v5.18-rc1-patched | | ------- | --------- | ----------------- | | 1 | 67.7 | 67.7 | | 2 | 67.7 | 67.7 | | 4 | 67.7 | 67.7 | | 8 | 67.7 | 67.7 | | 16 | 64.8 | 65.2 | | 32 | 59.8 | 62.8 | | 64 | 54.9 | 58.6 | | 128 | 49 | 55.8 | | 256 | 37.7 | 52.3 | | 512 | 31.8 | 51.4 | Yu Kuai (8): sbitmap: record the number of waiters for each waitqueue blk-mq: call 'bt_wait_ptr()' later in blk_mq_get_tag() sbitmap: make sure waitqueues are balanced blk-mq: don't preempt tag on heavy load sbitmap: force tag preemption if free tags are sufficient blk-mq: force tag preemption for split bios blk-mq: record how many tags are needed for splited bio sbitmap: wake up the number of threads based on required tags block/blk-merge.c | 9 ++- block/blk-mq-tag.c | 42 +++++++++----- block/blk-mq.c | 25 +++++++- block/blk-mq.h | 2 + include/linux/blk_types.h | 4 ++ include/linux/sbitmap.h | 9 +++ lib/sbitmap.c | 117 +++++++++++++++++++++++++------------- 7 files changed, 150 insertions(+), 58 deletions(-)