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=-7.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 35436C10F25 for ; Wed, 11 Mar 2020 07:51:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0FBED20873 for ; Wed, 11 Mar 2020 07:51:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728146AbgCKHvY (ORCPT ); Wed, 11 Mar 2020 03:51:24 -0400 Received: from lhrrgout.huawei.com ([185.176.76.210]:2548 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726472AbgCKHvY (ORCPT ); Wed, 11 Mar 2020 03:51:24 -0400 Received: from LHREML713-CAH.china.huawei.com (unknown [172.18.7.107]) by Forcepoint Email with ESMTP id 918DD3A2C4A2B82EA899; Wed, 11 Mar 2020 07:51:21 +0000 (GMT) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by LHREML713-CAH.china.huawei.com (10.201.108.36) with Microsoft SMTP Server (TLS) id 14.3.408.0; Wed, 11 Mar 2020 07:51:21 +0000 Received: from [127.0.0.1] (10.210.172.48) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.1713.5; Wed, 11 Mar 2020 07:51:19 +0000 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> <7bc94a9f-ec86-b343-0951-eba548c71b67@suse.de> From: John Garry Message-ID: Date: Wed, 11 Mar 2020 07:51:18 +0000 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: <7bc94a9f-ec86-b343-0951-eba548c71b67@suse.de> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.210.172.48] X-ClientProxiedBy: lhreml707-chm.china.huawei.com (10.201.108.56) 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 11/03/2020 06:58, 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. >> > Ah. Right. > Will be looking into that, and convert the patchset over to it. > Hannes, I assume that you will take back over this series now. Let me know. The patches are here, if not in patchwork: https://github.com/hisilicon/kernel-dev/tree/private-topic-sas-5.6-resv-commands-v2 > And the problem of the separate queue is the fact that I'll need a queue > to reserve tags from; trying to allocate a tag directly from the bitmap > turns out to be major surgery in the blocklayer with no immediate gain. > And I can't use per-device queues as for some drivers the reserved > commands are used to query the HBA itself to figure out how many devices > are present. Right, we still need to be able to allocate somewhere apart from sdev queue > Thanks