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 C5112C43334 for ; Mon, 13 Jun 2022 09:31:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234429AbiFMJbm (ORCPT ); Mon, 13 Jun 2022 05:31:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47678 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234476AbiFMJbk (ORCPT ); Mon, 13 Jun 2022 05:31:40 -0400 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 64D89186D8; Mon, 13 Jun 2022 02:31:37 -0700 (PDT) Received: from fraeml734-chm.china.huawei.com (unknown [172.18.147.206]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4LM5p33Dsxz67bVy; Mon, 13 Jun 2022 17:27:55 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml734-chm.china.huawei.com (10.206.15.215) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Mon, 13 Jun 2022 11:31:34 +0200 Received: from [10.195.33.253] (10.195.33.253) 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 15.1.2375.24; Mon, 13 Jun 2022 10:31:33 +0100 Message-ID: <53fa2856-54f2-c075-2eed-4f05c3459597@huawei.com> Date: Mon, 13 Jun 2022 10:34:41 +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 RFC v2 03/18] scsi: core: Implement reserved command handling To: Damien Le Moal , , , , , , CC: , , , , References: <1654770559-101375-1-git-send-email-john.garry@huawei.com> <1654770559-101375-4-git-send-email-john.garry@huawei.com> <7f80f3b6-84f6-de48-4e69-4562c96e62c5@huawei.com> From: John Garry In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.195.33.253] X-ClientProxiedBy: lhreml746-chm.china.huawei.com (10.201.108.196) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-ide@vger.kernel.org On 13/06/2022 10:06, Damien Le Moal wrote: >>> We cannot have more than 32 tags. >> We may have 32 regular tags and 1 reserved tag for SATA. > Right. But that is the messy part though. That extra 1 tag is actually not > a tag since all internal commands are non-NCQ commands that do not need a > tag... But apart from SATA, libsas LLDDs do need a real tag for the libata internal command. > > I am working on command duration limits support currently. This feature > set has a new horrendous "improvement": a command can be aborted by the > device if it fails its duration limit, but the abort is done with a good > status + sense data available bit set so that the device queue is not > aborted entirely like with a regular NCQ command error. > > For such aborted commands, the command sense data is set to > "COMPLETED/DATA UNAVAILABLE". In this case, the host needs to go read the > new "successful NCQ sense data log" to check that the command sense is > indeed "COMPLETED/DATA UNAVAILABLE". And to go read that log page without > stalling the device queue, we would need an internal NCQ (queuable) command. > > Currently, that is not possible to do cleanly as there are no guarantees > we can get a free tag (there is a race between block layer tag allocation > and libata internal tag counting). So a reserved tag for that would be > nice. We would end up with 31 IO tags at most + 1 reserved tag for NCQ > commands + ATA_TAG_INTERNAL for non-NCQ. That last one would be rendered > rather useless. But that also means that we kind-of go back to the days > when Linux showed ATA drives max QD of 31... So must the ATA_TAG_INTERNAL qc always be available for non-NCQ action like EH, and that is why you cannot reuse for this internal NCQ (queuable) command? > > I am still struggling with this particular use case and trying to make it > fit with your series. Trying out different things right now. > ok > >>> I think keeping can_queue as the max queue depth with at most >>> nr_reserved_cmds tags reserved is better. >> Maybe the wording in the comment can be improved as it originally >> focused on SAS HBAs where there are no special rules for tagset depth or >> how the tagset should be carved up to handle regular and reserved commands. > Indeed. And that would be for HBAs that do*not* use libsas/libata. > Otherwise, the NCQ vs non-NCQ reserved tag mess is there. > Thanks, John