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=-7.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 3507BC32750 for ; Tue, 13 Aug 2019 08:31:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 15A5A20663 for ; Tue, 13 Aug 2019 08:31:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728159AbfHMIbV (ORCPT ); Tue, 13 Aug 2019 04:31:21 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:4668 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727784AbfHMIbU (ORCPT ); Tue, 13 Aug 2019 04:31:20 -0400 Received: from DGGEMS404-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 1687FFF1F082E568E156; Tue, 13 Aug 2019 16:31:15 +0800 (CST) Received: from [127.0.0.1] (10.202.227.238) by DGGEMS404-HUB.china.huawei.com (10.3.19.204) with Microsoft SMTP Server id 14.3.439.0; Tue, 13 Aug 2019 16:31:03 +0800 Subject: Re: [PATCH 0/9] blk-mq/scsi: convert private reply queue into blk_mq hw queue To: Ming Lei , Jens Axboe , , , "Martin K . Petersen" References: <20190531022801.10003-1-ming.lei@redhat.com> CC: James Bottomley , Bart Van Assche , Hannes Reinecke , Don Brace , Kashyap Desai , "Sathya Prakash" , Christoph Hellwig , chenxiang From: John Garry Message-ID: Date: Tue, 13 Aug 2019 09:30:56 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.227.238] X-CFilter-Loop: Reflected Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 04/06/2019 09:49, John Garry wrote: > On 31/05/2019 03:27, Ming Lei wrote: >> Hi, Hi Ming, I'm raising the hostwide tags issue again, which I brought up in https://www.spinics.net/lists/linux-block/msg43754.html Here's that discussion: >> I don't mean to hijack this thread, but JFYI we're getting around to test >> https://github.com/ming1/linux/commits/v5.2-rc-host-tags-V2 - unfortunately >> we're still seeing a performance regression. I can't see where it's coming >> from. We're double-checking the test though. > > host-tag patchset is only for several particular drivers which use > private reply queue as completion queue. > > This patchset is for handling generic blk-mq CPU hotplug issue, and > the several particular scsi drivers(hisi_sas_v3, hpsa, megaraid_sas and > mp3sas) won't be covered so far. > > I'd suggest to move on for generic blk-mq devices first given now blk-mq > is the only request IO path now. > > There are at least two choices for us to handle drivers/devices with > private completion queue: > > 1) host-tags > - performance issue shouldn't be hard to solve, given it is same with > with single tags in theory, and just corner cases is there. > > What I am not glad with this approach is that blk-mq-tag code becomes mess. Right, not so neat. And we see a 3M vs 2.4M IOPS drop with this patchset. That's without any optimisation like discussed in https://lkml.org/lkml/2019/8/10/124 And I don't know about any impact of performance of hosts which already exposed multiple queues. Note that it's still much better than the 700K IOPS we see without managed interrupts at all. > > 2) private callback > - we could define private callback to drain each completion queue in > driver simply. Yeah, but then we raise the question of why the LLDD can't just register for hotplug handler itself. Personally I prefer #1. I'll have a look at the issues when I get a chance. Much appreciated, John