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 C7452C33CB1 for ; Tue, 14 Jan 2020 13:57:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A2814214AF for ; Tue, 14 Jan 2020 13:57:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726450AbgANN5M (ORCPT ); Tue, 14 Jan 2020 08:57:12 -0500 Received: from lhrrgout.huawei.com ([185.176.76.210]:2267 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726115AbgANN5M (ORCPT ); Tue, 14 Jan 2020 08:57:12 -0500 Received: from lhreml707-cah.china.huawei.com (unknown [172.18.7.108]) by Forcepoint Email with ESMTP id DD3B4B0CEBEA626A9554; Tue, 14 Jan 2020 13:57:09 +0000 (GMT) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by lhreml707-cah.china.huawei.com (10.201.108.48) with Microsoft SMTP Server (TLS) id 14.3.408.0; Tue, 14 Jan 2020 13:57:09 +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; Tue, 14 Jan 2020 13:57:09 +0000 Subject: Re: [PATCH 09/11] megaraid_sas: switch fusion adapters to MQ From: John Garry 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> <1383a868-76d8-5c26-556d-7374e189b7ce@huawei.com> Message-ID: <71cf0932-ab93-675c-4d7c-37889c003468@huawei.com> Date: Tue, 14 Jan 2020 13:57:08 +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: <1383a868-76d8-5c26-556d-7374e189b7ce@huawei.com> 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 12:09, John Garry 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. Hi Ming, I think that your questions here were related to the shared scheduler tags, which was Hannes' proposal (I initially had it in v2 series, but dropped it for v3). I was just content to maintain the concept of shared driver tags. Thanks, John > >> >>> 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