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=-7.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 E0F16C2BB55 for ; Tue, 7 Apr 2020 11:54:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C12F42074B for ; Tue, 7 Apr 2020 11:54:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728478AbgDGLyy (ORCPT ); Tue, 7 Apr 2020 07:54:54 -0400 Received: from lhrrgout.huawei.com ([185.176.76.210]:2635 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726562AbgDGLyy (ORCPT ); Tue, 7 Apr 2020 07:54:54 -0400 Received: from lhreml724-chm.china.huawei.com (unknown [172.18.7.106]) by Forcepoint Email with ESMTP id 159A3B05CDA06F27F690; Tue, 7 Apr 2020 12:54:52 +0100 (IST) Received: from [127.0.0.1] (10.210.168.238) 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 15.1.1913.5; Tue, 7 Apr 2020 12:54:50 +0100 Subject: Re: [PATCH RFC v2 02/24] scsi: allocate separate queue for reserved commands To: Hannes Reinecke , Christoph Hellwig CC: , , , , , , , , , , , Hannes Reinecke References: <1583857550-12049-1-git-send-email-john.garry@huawei.com> <1583857550-12049-3-git-send-email-john.garry@huawei.com> <20200310183243.GA14549@infradead.org> <79cf4341-f2a2-dcc9-be0d-2efc6e83028a@huawei.com> <20200311062228.GA13522@infradead.org> From: John Garry Message-ID: <9c6ced82-b3f1-9724-b85e-d58827f1a4a4@huawei.com> Date: Tue, 7 Apr 2020 12:54:29 +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: [10.210.168.238] X-ClientProxiedBy: lhreml738-chm.china.huawei.com (10.201.108.188) 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 06/04/2020 10:05, Hannes Reinecke wrote: > On 3/11/20 7:22 AM, Christoph Hellwig wrote: >> On Tue, Mar 10, 2020 at 09:08:56PM +0000, John Garry wrote: >>> On 10/03/2020 18:32, Christoph Hellwig wrote: >>>> On Wed, Mar 11, 2020 at 12:25:28AM +0800, John Garry wrote: >>>>> From: Hannes Reinecke >>>>> >>>>> Allocate a separate 'reserved_cmd_q' for sending reserved commands. >>>> >>>> Why? Reserved command specifically are not in any way tied to queues. >>>> . >>>> >>> >>> So the v1 series used a combination of the sdev queue and the per-host >>> reserved_cmd_q. Back then you questioned using the sdev queue for virtio >>> scsi, and the unconfirmed conclusion was to use a common per-host q. This is >>> the best link I can find now: >>> >>> https://www.mail-archive.com/linux-scsi@vger.kernel.org/msg83177.html >> >> That was just a question on why virtio uses the per-device tags, which >> didn't look like it made any sense. What I'm worried about here is >> mixing up the concept of reserved tags in the tagset, and queues to use >> them. Note that we already have the scsi_get_host_dev to allocate >> a scsi_device and thus a request_queue for the host itself. That seems >> like the better interface to use a tag for a host wide command vs >> introducing a parallel path. >> > Thinking about it some more, I don't think that scsi_get_host_dev() is > the best way of handling it. > Problem is that it'll create a new scsi_device with , > which will then show up via eg 'lsscsi'. are you sure? Doesn't this function just allocate the sdev, but do nothing with it, like probing it? I bludgeoned it in here for PoC: https://github.com/hisilicon/kernel-dev/commit/ef0ae8540811e32776f64a5b42bd76cbed17ba47 And then still: john@ubuntu:~$ lsscsi [0:0:0:0] disk SEAGATE ST2000NM0045 N004 /dev/sda [0:0:1:0] disk SEAGATE ST2000NM0045 N004 /dev/sdb [0:0:2:0] disk ATASAMSUNG HM320JI 0_01 /dev/sdc [0:0:3:0] disk SEAGATE ST1000NM0023 0006 /dev/sdd [0:0:4:0] enclosu HUAWEIExpander 12Gx16 128- john@ubuntu:~$ Some proper plumbing would be needed, though. > This would be okay if 'this_id' would have been defined by the driver; > sadly, most drivers which are affected here do set 'this_id' to -1. > So we wouldn't have a nice target ID to allocate the device from, let > alone the problem that we would have to emulate a complete scsi device > with all required minimal command support etc. > And I'm not quite sure how well that would play with the exising SCSI > host template; the device we'll be allocating would have basically > nothing in common with the 'normal' SCSI devices. > > What we could do, though, is to try it the other way round: > Lift the request queue from scsi_get_host_dev() into the scsi host > itself, so that scsi_get_host_dev() can use that queue, but we also > would be able to use it without a SCSI device attached. wouldn't that limit 1x scsi device per host, not that I know if any more would ever be required? But it does still seem better to use the request queue in the scsi device. > cheers, John From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Garry Subject: Re: [PATCH RFC v2 02/24] scsi: allocate separate queue for reserved commands Date: Tue, 7 Apr 2020 12:54:29 +0100 Message-ID: <9c6ced82-b3f1-9724-b85e-d58827f1a4a4@huawei.com> References: <1583857550-12049-1-git-send-email-john.garry@huawei.com> <1583857550-12049-3-git-send-email-john.garry@huawei.com> <20200310183243.GA14549@infradead.org> <79cf4341-f2a2-dcc9-be0d-2efc6e83028a@huawei.com> <20200311062228.GA13522@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Hannes Reinecke , Christoph Hellwig Cc: axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com, ming.lei@redhat.com, bvanassche@acm.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, virtualization@lists.linux-foundation.org, esc.storagedev@microsemi.com, chenxiang66@hisilicon.com, Hannes Reinecke List-Id: virtualization@lists.linuxfoundation.org On 06/04/2020 10:05, Hannes Reinecke wrote: > On 3/11/20 7:22 AM, Christoph Hellwig wrote: >> On Tue, Mar 10, 2020 at 09:08:56PM +0000, John Garry wrote: >>> On 10/03/2020 18:32, Christoph Hellwig wrote: >>>> On Wed, Mar 11, 2020 at 12:25:28AM +0800, John Garry wrote: >>>>> From: Hannes Reinecke >>>>> >>>>> Allocate a separate 'reserved_cmd_q' for sending reserved commands. >>>> >>>> Why? Reserved command specifically are not in any way tied to queues. >>>> . >>>> >>> >>> So the v1 series used a combination of the sdev queue and the per-host >>> reserved_cmd_q. Back then you questioned using the sdev queue for virtio >>> scsi, and the unconfirmed conclusion was to use a common per-host q. This is >>> the best link I can find now: >>> >>> https://www.mail-archive.com/linux-scsi@vger.kernel.org/msg83177.html >> >> That was just a question on why virtio uses the per-device tags, which >> didn't look like it made any sense. What I'm worried about here is >> mixing up the concept of reserved tags in the tagset, and queues to use >> them. Note that we already have the scsi_get_host_dev to allocate >> a scsi_device and thus a request_queue for the host itself. That seems >> like the better interface to use a tag for a host wide command vs >> introducing a parallel path. >> > Thinking about it some more, I don't think that scsi_get_host_dev() is > the best way of handling it. > Problem is that it'll create a new scsi_device with , > which will then show up via eg 'lsscsi'. are you sure? Doesn't this function just allocate the sdev, but do nothing with it, like probing it? I bludgeoned it in here for PoC: https://github.com/hisilicon/kernel-dev/commit/ef0ae8540811e32776f64a5b42bd76cbed17ba47 And then still: john@ubuntu:~$ lsscsi [0:0:0:0] disk SEAGATE ST2000NM0045 N004 /dev/sda [0:0:1:0] disk SEAGATE ST2000NM0045 N004 /dev/sdb [0:0:2:0] disk ATASAMSUNG HM320JI 0_01 /dev/sdc [0:0:3:0] disk SEAGATE ST1000NM0023 0006 /dev/sdd [0:0:4:0] enclosu HUAWEIExpander 12Gx16 128- john@ubuntu:~$ Some proper plumbing would be needed, though. > This would be okay if 'this_id' would have been defined by the driver; > sadly, most drivers which are affected here do set 'this_id' to -1. > So we wouldn't have a nice target ID to allocate the device from, let > alone the problem that we would have to emulate a complete scsi device > with all required minimal command support etc. > And I'm not quite sure how well that would play with the exising SCSI > host template; the device we'll be allocating would have basically > nothing in common with the 'normal' SCSI devices. > > What we could do, though, is to try it the other way round: > Lift the request queue from scsi_get_host_dev() into the scsi host > itself, so that scsi_get_host_dev() can use that queue, but we also > would be able to use it without a SCSI device attached. wouldn't that limit 1x scsi device per host, not that I know if any more would ever be required? But it does still seem better to use the request queue in the scsi device. > cheers, John