Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752458AbeAQKO5 (ORCPT + 1 other); Wed, 17 Jan 2018 05:14:57 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:58918 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750830AbeAQKOz (ORCPT ); Wed, 17 Jan 2018 05:14:55 -0500 Subject: Re: [PATCH 2/2] blk-mq: simplify queue mapping & schedule with each possisble CPU From: Christian Borntraeger To: Ming Lei , "jianchao.wang" Cc: linux-block@vger.kernel.org, Keith Busch , Sagi Grimberg , Christoph Hellwig , Stefan Haberland , linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, James Smart , Jens Axboe , Thomas Gleixner , Christoph Hellwig References: <20180112025306.28004-3-ming.lei@redhat.com> <0d36c16b-cb4b-6088-fdf3-2fe5d8f33cd7@oracle.com> <20180116121010.GA26429@ming.t460p> <7c24e321-2d3b-cdec-699a-f58c34300aa9@oracle.com> <20180116153248.GA3018@ming.t460p> <7f5bad86-febc-06fc-67c0-393777d172e4@oracle.com> <20180117035159.GA9487@ming.t460p> <8c8efce8-ea02-0a9e-8369-44c885f4731d@oracle.com> <20180117062251.GC9487@ming.t460p> <977e9c62-c7f2-d1df-7d6b-5903f3b21cb6@oracle.com> <20180117095744.GF9487@ming.t460p> Date: Wed, 17 Jan 2018 11:14:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18011710-0040-0000-0000-00000405B4B9 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18011710-0041-0000-0000-0000260924D0 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-01-17_03:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1801170149 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On 01/17/2018 11:07 AM, Christian Borntraeger wrote: > > > On 01/17/2018 10:57 AM, Ming Lei wrote: >> Hi Jianchao, >> >> On Wed, Jan 17, 2018 at 04:09:11PM +0800, jianchao.wang wrote: >>> Hi ming >>> >>> Thanks for your kindly response. >>> >>> On 01/17/2018 02:22 PM, Ming Lei wrote: >>>> This warning can't be removed completely, for example, the CPU figured >>>> in blk_mq_hctx_next_cpu(hctx) can be put on again just after the >>>> following call returns and before __blk_mq_run_hw_queue() is scheduled >>>> to run. >>>> >>>> kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work, msecs_to_jiffies(msecs)) >>> We could use cpu_active in __blk_mq_run_hw_queue() to narrow the window. >>> There is a big gap between cpu_online and cpu_active. rebind_workers is also between them. >> >> This warning is harmless, also you can't reproduce it without help of your >> special patch, I guess, :-) So the window shouldn't be a big deal. > > FWIW, every WARN_ON is problematic since there are people running with panic_on_warn. To make it more clear. Every WARN_ON that can happen in real life without actually being an error is problematic. > If a condition can happen we should not use WARN_ON but something else. >