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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS 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 E2834C43381 for ; Mon, 1 Apr 2019 09:19:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ADC26213A2 for ; Mon, 1 Apr 2019 09:19:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="KNs5YV0F" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726604AbfDAJTU (ORCPT ); Mon, 1 Apr 2019 05:19:20 -0400 Received: from aserp2130.oracle.com ([141.146.126.79]:33518 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725821AbfDAJTT (ORCPT ); Mon, 1 Apr 2019 05:19:19 -0400 Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x3194Cik091650; Mon, 1 Apr 2019 09:19:05 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=XRl1QmEdNWQV5dsmWsJ5qr3weJMDJFoO6g5XRJBflmI=; b=KNs5YV0FyJ6Sc1X6tu23eW2RvQ31/to/+IZRHtAKt+x9FW3JDNHunZ0mlXkdcKMHM5jx 5sJ2QthaWg9Tt4wrjE+G0pBhuOvsweP8VolYlWVkYzpn3Dn4A+iFU/tX35IxlbvzNwn6 wZq0TkNUlE9i+yMXSfAgRSRMf0vjzLOC2d1jKRqJGIeJisKeKJJOYKCaOnottrIylQm4 B//ZcdAJq+XYD7GphySIK5KgF/146/or+2qLLRItq8qDryJnqjDxkWB96rHfLhKtkiyG 29UG3DO51ggH5yVjRlAtaD0euWXp4Sq/kCE5dp6r6su2MSdewW/4OPidTYJXcXMvzZtD Ew== Received: from userv0021.oracle.com (userv0021.oracle.com [156.151.31.71]) by aserp2130.oracle.com with ESMTP id 2rhwycwwp5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 01 Apr 2019 09:19:05 +0000 Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id x319IsXP023178 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 1 Apr 2019 09:18:54 GMT Received: from abhmp0003.oracle.com (abhmp0003.oracle.com [141.146.116.9]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x319Iqjh002759; Mon, 1 Apr 2019 09:18:52 GMT Received: from [10.182.71.8] (/10.182.71.8) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 01 Apr 2019 02:18:52 -0700 Subject: Re: [PATCH 0/5] blk-mq: allow to run queue if queue refcount is held To: Ming Lei Cc: Bart Van Assche , Jens Axboe , linux-block@vger.kernel.org, James Smart , Bart Van Assche , linux-scsi@vger.kernel.org, "Martin K . Petersen" , Christoph Hellwig , "James E . J . Bottomley" References: <20190331030954.22320-1-ming.lei@redhat.com> <10c8ed10-3c96-b73c-18d8-114773b1d675@acm.org> <20190401020036.GB30776@ming.t460p> <20190401025237.GE30776@ming.t460p> <21b2000b-16b6-f5a6-692b-73143a49a4ec@oracle.com> <20190401032852.GG30776@ming.t460p> From: "jianchao.wang" Message-ID: Date: Mon, 1 Apr 2019 17:19:01 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190401032852.GG30776@ming.t460p> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9213 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904010065 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi Ming On 4/1/19 11:28 AM, Ming Lei wrote: > On Mon, Apr 01, 2019 at 11:25:50AM +0800, jianchao.wang wrote: >> Hi Ming >> >> On 4/1/19 10:52 AM, Ming Lei wrote: >>>> percpu_ref_tryget_live() fails if a per-cpu counter is in the "dead" state. >>>> percpu_ref_kill() changes the state of a per-cpu counter to the "dead" >>>> state. blk_freeze_queue_start() calls percpu_ref_kill(). blk_cleanup_queue() >>>> already calls blk_set_queue_dying() and that last function calls >>>> blk_freeze_queue_start(). So I think that what you wrote is not correct and >>>> that inserting a percpu_ref_tryget_live()/percpu_ref_put() pair in >>>> blk_mq_run_hw_queues() or blk_mq_run_hw_queue() would make a difference and >>>> also that moving the percpu_ref_exit() call into blk_release_queue() makes >>>> sense. >>> If percpu_ref_exit() is moved to blk_release_queue(), we still need to >>> move freeing of hw queue's resource into blk_release_queue() like what >>> the patchset is doing. >>> >>> Then we don't need to get/put q_usage_counter in blk_mq_run_hw_queues() any more, >>> do we? >> >> IMO, if we could get a way to prevent any attempt to run queue, it would be >> better and clearer. > > It is hard to do that way, and not necessary. > > I will post V2 soon for review. > Put percpu_ref_tryget/put pair into blk_mq_run_hw_queues could stop run queue after requet_queue is frozen and drained (run queue is also unnecessary because there is no entered requests). And also percpu_ref_tryget could avoid the io hung issue you mentioned. We have similar one in blk_mq_timeout_work. freeze and drain queue to stop new attempt to run queue, blk_sync_queue syncs and stops the started ones, then hctx->run_queue is cleaned totally. IMO, it would be better to have a checkpoint after which there will be no any in-flight asynchronous activities of the request_queue (hctx->run_work, q->requeue_work, q-> timeout_work) and any attempt to start them will fail. Perhaps, this will be a good change to do this ；） Thanks Jianchao