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: Wed, 11 Mar 2020 07:51:18 +0000 Message-ID: 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> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <7bc94a9f-ec86-b343-0951-eba548c71b67@suse.de> Content-Language: en-US Sender: linux-block-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 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