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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 3C6A8C18E5A for ; Tue, 10 Mar 2020 21:09:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0A11224649 for ; Tue, 10 Mar 2020 21:09:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726411AbgCJVJB (ORCPT ); Tue, 10 Mar 2020 17:09:01 -0400 Received: from lhrrgout.huawei.com ([185.176.76.210]:2547 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726268AbgCJVJB (ORCPT ); Tue, 10 Mar 2020 17:09:01 -0400 Received: from lhreml705-cah.china.huawei.com (unknown [172.18.7.106]) by Forcepoint Email with ESMTP id B0422B53C758ABD6007B; Tue, 10 Mar 2020 21:08:59 +0000 (GMT) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by lhreml705-cah.china.huawei.com (10.201.108.46) with Microsoft SMTP Server (TLS) id 14.3.408.0; Tue, 10 Mar 2020 21:08:59 +0000 Received: from [127.0.0.1] (10.210.167.10) 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 15.1.1713.5; Tue, 10 Mar 2020 21:08:57 +0000 Subject: Re: [PATCH RFC v2 02/24] scsi: allocate separate queue for reserved commands To: 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> From: John Garry Message-ID: <79cf4341-f2a2-dcc9-be0d-2efc6e83028a@huawei.com> Date: Tue, 10 Mar 2020 21:08:56 +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: <20200310183243.GA14549@infradead.org> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.210.167.10] X-ClientProxiedBy: lhreml726-chm.china.huawei.com (10.201.108.77) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org 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 " >> My implementation actually allows for per-device reserved tags (eg for >> virtio). But some drivers require to use internal commands prior to any >> device setup, so they have to use a separate reserved command queue just to >> be able to allocate tags. > > Why would virtio-scsi need per-device reserved commands? It currently uses > a global mempool to allocate the reset commands. > Oh, I'm perfectly fine with dropping the per-device reserved commands, and use the host-wide queue in general. It turns out most of the drivers use it that way already. Will be doing so for the next iteration. " Cheers