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,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 1A3F8C33CA2 for ; Fri, 10 Jan 2020 12:09:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E0AE32072A for ; Fri, 10 Jan 2020 12:09:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727949AbgAJMJc (ORCPT ); Fri, 10 Jan 2020 07:09:32 -0500 Received: from lhrrgout.huawei.com ([185.176.76.210]:2252 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727841AbgAJMJb (ORCPT ); Fri, 10 Jan 2020 07:09:31 -0500 Received: from LHREML710-CAH.china.huawei.com (unknown [172.18.7.106]) by Forcepoint Email with ESMTP id 45794362A9D96309B557; Fri, 10 Jan 2020 12:09:30 +0000 (GMT) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by LHREML710-CAH.china.huawei.com (10.201.108.33) with Microsoft SMTP Server (TLS) id 14.3.408.0; Fri, 10 Jan 2020 12:09:29 +0000 Received: from [127.0.0.1] (10.202.226.43) 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 15.1.1713.5; Fri, 10 Jan 2020 12:09:29 +0000 Subject: Re: [PATCH 09/11] megaraid_sas: switch fusion adapters to MQ To: Ming Lei CC: Sumit Saxena , Hannes Reinecke , "Martin K. Petersen" , Jens Axboe , Christoph Hellwig , James Bottomley , Linux SCSI List , , Hannes Reinecke References: <20191202153914.84722-1-hare@suse.de> <20191202153914.84722-10-hare@suse.de> <339f089f-26aa-1cbe-416b-67809ea6791f@huawei.com> <20200110020038.GB4501@ming.t460p> From: John Garry Message-ID: <1383a868-76d8-5c26-556d-7374e189b7ce@huawei.com> Date: Fri, 10 Jan 2020 12:09:28 +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: <20200110020038.GB4501@ming.t460p> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.226.43] X-ClientProxiedBy: lhreml729-chm.china.huawei.com (10.201.108.80) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 10/01/2020 02:00, Ming Lei wrote: > On Thu, Jan 09, 2020 at 11:55:12AM +0000, John Garry wrote: >> On 09/12/2019 10:10, Sumit Saxena wrote: >>> On Mon, Dec 2, 2019 at 9:09 PM Hannes Reinecke wrote: >>>> >>>> Fusion adapters can steer completions to individual queues, and >>>> we now have support for shared host-wide tags. >>>> So we can enable multiqueue support for fusion adapters and >>>> drop the hand-crafted interrupt affinity settings. >>> >>> Hi Hannes, >>> >>> Ming Lei also proposed similar changes in megaraid_sas driver some >>> time back and it had resulted in performance drop- >>> https://patchwork.kernel.org/patch/10969511/ >>> >>> So, we will do some performance tests with this patch and update you. >>> >> >> Hi Sumit, >> >> I was wondering if you had a chance to do this test yet? >> >> It would be good to know, so we can try to progress this work. > > Looks most of the comment in the following link isn't addressed: > > https://lore.kernel.org/linux-block/20191129002540.GA1829@ming.t460p/ OK, but I was waiting for results first, which I hoped would not take too long. They weren't forgotten, for sure. Let me check them now. > >> Firstly too much((nr_hw_queues - 1) times) memory is wasted. Secondly IO >> latency could be increased by too deep scheduler queue depth. Finally CPU >> could be wasted in the retrying of running busy hw queue. >> >> Wrt. driver tags, this patch may be worse, given the average limit for >> each LUN is reduced by (nr_hw_queues) times, see hctx_may_queue(). >> >> Another change is bt_wait_ptr(). Before your patches, there is single >> .wait_index, now the number of .wait_index is changed to nr_hw_queues. >> >> Also the run queue number is increased a lot in SCSI's IO completion, see >> scsi_end_request(). > > I guess memory waste won't be a blocker. Yeah, that's a trade-off. And, as I remember, memory waste does not seem extreme. > > But it may not be one accepted behavior to reduce average active queue > depth for each LUN by nr_hw_queues times, meantime scheduler queue depth > is increased by nr_hw_queues times, compared with single queue. > Thanks, John