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 F296BC433ED for ; Tue, 27 Apr 2021 10:19:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C60D3613C3 for ; Tue, 27 Apr 2021 10:19:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235488AbhD0KUa (ORCPT ); Tue, 27 Apr 2021 06:20:30 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:2924 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238178AbhD0KSy (ORCPT ); Tue, 27 Apr 2021 06:18:54 -0400 Received: from fraeml743-chm.china.huawei.com (unknown [172.18.147.201]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4FTyB14YMhz73dSD; Tue, 27 Apr 2021 18:07:37 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml743-chm.china.huawei.com (10.206.15.224) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Tue, 27 Apr 2021 12:18:09 +0200 Received: from [10.47.94.234] (10.47.94.234) 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 15.1.2176.2; Tue, 27 Apr 2021 11:18:08 +0100 Subject: Re: [bug report] shared tags causes IO hang and performance drop To: Ming Lei CC: Kashyap Desai , , , "Martin K. Petersen" , Jens Axboe , Douglas Gilbert , Hannes Reinecke References: <0c85fe52-ebc7-68b3-2dbe-dfad5d604346@huawei.com> <55743a51-4d6f-f481-cebf-e2af9c657911@huawei.com> <9ad15067-ba7b-a335-ae71-8c4328856b91@huawei.com> From: John Garry Message-ID: <440dfcfc-1a2c-bd98-1161-cec4d78c6dfc@huawei.com> Date: Tue, 27 Apr 2021 11:15:09 +0100 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: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.47.94.234] X-ClientProxiedBy: lhreml745-chm.china.huawei.com (10.201.108.195) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 27/04/2021 10:52, Ming Lei wrote: >> BTW, for the performance issue which Yanhui witnessed with megaraid sas, do >> you think it may because of the IO sched tags issue of total sched tag depth >> growing vs driver tags? > I think it is highly possible. Will you work a patch to convert to > per-request-queue sched tag? > Sure, I'm just hacking now to see what difference it can make to performance. Early results look promising... >> Are there lots of LUNs? I can imagine that megaraid >> sas has much larger can_queue than scsi_debug:) > No, there are just two LUNs, the 1st LUN is one commodity SSD(queue > depth is 32) and the performance issue is reported on this LUN, another is one > HDD(queue depth is 256) which is root disk, but the megaraid host tag depth is > 228, another weird setting. But the issue still can be reproduced after we set > 2nd LUN's depth as 64 for avoiding driver tag contention. > > BTW, one more thing which Kashyap and I looked at when initially developing the hostwide tag support was the wait struct usage in tag exhaustion scenario: https://lore.kernel.org/linux-block/ecaeccf029c6fe377ebd4f30f04df9f1@mail.gmail.com/ IIRC, we looked at a "hostwide" wait_index - it didn't seem to make a difference then, and we didn't end up make any changes here, but still worth remembering. Thanks, John