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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,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 3F7D1C433E0 for ; Tue, 12 Jan 2021 08:58:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E00D8208E4 for ; Tue, 12 Jan 2021 08:58:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392434AbhALI6g (ORCPT ); Tue, 12 Jan 2021 03:58:36 -0500 Received: from frasgout.his.huawei.com ([185.176.79.56]:2309 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727916AbhALI6f (ORCPT ); Tue, 12 Jan 2021 03:58:35 -0500 Received: from fraeml712-chm.china.huawei.com (unknown [172.18.147.201]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4DFPV91R3Tz67b8F; Tue, 12 Jan 2021 16:52:49 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml712-chm.china.huawei.com (10.206.15.61) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Tue, 12 Jan 2021 09:57:53 +0100 Received: from [10.210.171.61] (10.210.171.61) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Tue, 12 Jan 2021 08:57:52 +0000 Subject: Re: About scsi device queue depth To: Ming Lei CC: Bart Van Assche , Hannes Reinecke , Kashyap Desai , "Martin K . Petersen" , "James E.J. Bottomley" , Christoph Hellwig , "linux-scsi@vger.kernel.org" , Sathya Prakash , Sreekanth Reddy , Suganath Prabu Subramani , PDL-MPT-FUSIONLINUX , chenxiang References: <9ff894da-cf2c-9094-2690-1973cc57835a@huawei.com> <20210112014203.GA60605@T590> From: John Garry Message-ID: <4b50f067-a368-2197-c331-a8c981f5cd02@huawei.com> Date: Tue, 12 Jan 2021 08:56:45 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: <20210112014203.GA60605@T590> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.210.171.61] X-ClientProxiedBy: lhreml744-chm.china.huawei.com (10.201.108.194) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org Hi Ming, >> >> I was looking at some IOMMU issue on a LSI RAID 3008 card, and noticed that >> performance there is not what I get on other SAS HBAs - it's lower. >> >> After some debugging and fiddling with sdev queue depth in mpt3sas driver, I >> am finding that performance changes appreciably with sdev queue depth: >> >> sdev qdepth fio number jobs* 1 10 20 >> 16 1590 1654 1660 >> 32 1545 1646 1654 >> 64 1436 1085 1070 >> 254 (default) 1436 1070 1050 > > What does the performance number mean? IOPS or others? What is the fio > io test? random IO or sequential IO? So those figures are x1K IOPs read performance; so 1590, above, is 1.59M IOPs read. Here's the fio script: [global] rw=read direct=1 ioengine=libaio iodepth=40 numjobs=20 bs=4k ;size=10240000m ;zero_buffers=1 group_reporting=1 ;ioscheduler=noop ;cpumask=0xffe ;cpus_allowed=1-47 ;gtod_reduce=1 ;iodepth_batch=2 ;iodepth_batch_complete=2 runtime=60 ;thread loops = 10000 >> >> fio queue depth is 40, and I'm using 12x SAS SSDs. >> >> I got comparable disparity in results for fio queue depth = 128 and num jobs >> = 1: >> >> sdev qdepth fio number jobs* 1 >> 16 1640 >> 32 1618 >> 64 1577 >> 254 (default) 1437 >> >> IO sched = none. >> >> That driver also sets queue depth tracking = 1, but never seems to kick in. >> >> So it seems to me that the block layer is merging more bios per request, as >> averge sg count per request goes up from 1 - > upto 6 or more. As I see, >> when queue depth lowers the only thing that is really changing is that we >> fail more often in getting the budget in >> scsi_mq_get_budget()->scsi_dev_queue_ready(). > > Right, the behavior basically doesn't change compared with block legacy > io path. And that is why sdev->queue_depth is a bit important for HDD. OK > >> >> So initial sdev queue depth comes from cmd_per_lun by default or manually >> setting in the driver via scsi_change_queue_depth(). It seems to me that >> some drivers are not setting this optimally, as above. >> >> Thoughts on guidance for setting sdev queue depth? Could blk-mq changed this >> behavior? > > So far, the sdev queue depth is provided by SCSI layer, and blk-mq can > queue one request only if budget is obtained via .get_budget(). > Well, based on my testing, default sdev queue depth seems too large for that LLDD ... Thanks, John