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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D169EFA3740 for ; Tue, 25 Oct 2022 11:36:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229904AbiJYLgQ (ORCPT ); Tue, 25 Oct 2022 07:36:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51004 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229744AbiJYLgP (ORCPT ); Tue, 25 Oct 2022 07:36:15 -0400 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE3046CD10; Tue, 25 Oct 2022 04:36:14 -0700 (PDT) Received: from fraeml735-chm.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4MxVD96hy0z686Kq; Tue, 25 Oct 2022 19:32:41 +0800 (CST) Received: from lhrpeml500003.china.huawei.com (7.191.162.67) by fraeml735-chm.china.huawei.com (10.206.15.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Tue, 25 Oct 2022 13:36:12 +0200 Received: from [10.48.144.83] (10.48.144.83) by lhrpeml500003.china.huawei.com (7.191.162.67) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Tue, 25 Oct 2022 12:36:11 +0100 Message-ID: <05ae5abd-9b96-3ffe-6bd9-e996d28a8897@huawei.com> Date: Tue, 25 Oct 2022 12:36:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH] blk-mq: Properly init bios from blk_mq_alloc_request_hctx() To: Ming Lei CC: , , , , Bart Van Assche References: <99c6ca81-746d-85f4-04d3-49d7a3de611b@huawei.com> <360c78dc-65ce-362f-389d-075f2259ce5b@huawei.com> <3513b14c-14e0-b865-628e-a83521090de9@huawei.com> <399a2c2d-0b56-e4e7-c309-a6b9537d8939@huawei.com> From: John Garry In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.48.144.83] X-ClientProxiedBy: lhrpeml100005.china.huawei.com (7.191.160.25) To lhrpeml500003.china.huawei.com (7.191.162.67) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 25/10/2022 12:21, Ming Lei wrote: >> Actually if final cpu in hctx->cpumask is going offline, then hctx won't >> queue any more requests, right? In this case I don't think we can queue on >> that hctx anyway. I need to think about this more. > It can be queued actually, but interrupt may not be delivered if managed > irq is used. Yes, I think it will be queued elsewhere. I would need to check the code again. > >>> If you just make it one driver private command, there can't be such >>> issue. >> Well we're trying to use reserved requests for EH commands, which that goes >> against. >> >>> Block layer is supposed for handling common case(normal io and pt io), >>> I'd suggest to not put such special cases into block layer. >> It also supports reserved commands, which I would assume would be suitable >> for EH scenarios. > Then you have to be careful, as I mentioned, EH has to provide forward > progress, if you let blk-mq allocate & submit EH request, the implied > dependency from blk-mq has to be payed attention. OK, thanks, I know that this carries risk, but it seems right approach. I have been thinking about my HW queue allocation requirement and maybe we can solve in low-level driver instead. The requirement is to send this abort command on same queue as erroneous command to ensure that they do not race in HW submission, even though chance of this is really tiny. Maybe we can make low-level driver wait until erroneous command is really submitted to HW by checking HW register, etc. before issuing abort on any HW queue (and so would not need blk_mq_alloc_request_hctx() or similar). BTW, I would still like to fix blk_mq_alloc_request_hctx() to properly init ->bio and other fields - ok? Thanks, John