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 EDE95C433FE for ; Wed, 23 Mar 2022 09:01:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243021AbiCWJDM (ORCPT ); Wed, 23 Mar 2022 05:03:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42188 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234009AbiCWJDK (ORCPT ); Wed, 23 Mar 2022 05:03:10 -0400 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 326116EB0D; Wed, 23 Mar 2022 02:01:40 -0700 (PDT) Received: from fraeml743-chm.china.huawei.com (unknown [172.18.147.226]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4KNj3b1ngBz67PtB; Wed, 23 Mar 2022 16:59:55 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml743-chm.china.huawei.com (10.206.15.224) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Wed, 23 Mar 2022 10:01:37 +0100 Received: from [10.47.85.68] (10.47.85.68) 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 15.1.2308.21; Wed, 23 Mar 2022 09:01:36 +0000 Message-ID: <378065de-3cb8-b44f-66e9-747960bcd990@huawei.com> Date: Wed, 23 Mar 2022 09:01:33 +0000 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 01/11] blk-mq: Add blk_mq_init_queue_ops() To: Bart Van Assche , , , , , , , CC: , , , , , , References: <1647945585-197349-1-git-send-email-john.garry@huawei.com> <1647945585-197349-2-git-send-email-john.garry@huawei.com> From: John Garry In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.47.85.68] X-ClientProxiedBy: lhreml730-chm.china.huawei.com (10.201.108.81) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/03/2022 02:57, Bart Van Assche wrote: > On 3/22/22 03:39, John Garry wrote: >> Add an API to allocate a request queue which accepts a custom set of >> blk_mq_ops for that request queue. >> >> The reason which we may want custom ops is for queuing requests which we >> don't want to go through the normal queuing path. > Hi Bart, > Custom ops shouldn't be required for this. See e.g. how tmf_queue > is used in the UFS driver for an example of a queue implementation > with custom operations and that does not require changes of the block > layer core. The UFS code uses a private tagset (in ufs_hba.tmf_tag_set) for only management of TMF tags/memories. This tagset does not really have any custom operations. All it has is a stub of .queue_rq CB in ufshcd_queue_tmf() and that is because this CB is compulsory. As for the idea of having multiple tagsets per shost with real custom operations, this idea was mentioned before, but I think managing multiple tagsets could be trouble. For a start, it would mean that we need a distinct allocation of reserved and regular tags, and sometimes we don't want this - as Hannes mentioned earlier, many HBAs have low queue depth and cannot afford to permanently carve out a bunch of reserved tags. Thanks, John