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Wed, 11 Mar 2020 06:58:50 +0000 (UTC) Subject: Re: [PATCH RFC v2 02/24] scsi: allocate separate queue for reserved commands To: Christoph Hellwig , John Garry 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 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> From: Hannes Reinecke Openpgp: preference=signencrypt Autocrypt: addr=hare@suse.de; prefer-encrypt=mutual; keydata= mQINBE6KyREBEACwRN6XKClPtxPiABx5GW+Yr1snfhjzExxkTYaINHsWHlsLg13kiemsS6o7 qrc+XP8FmhcnCOts9e2jxZxtmpB652lxRB9jZE40mcSLvYLM7S6aH0WXKn8bOqpqOGJiY2bc 6qz6rJuqkOx3YNuUgiAxjuoYauEl8dg4bzex3KGkGRuxzRlC8APjHlwmsr+ETxOLBfUoRNuE b4nUtaseMPkNDwM4L9+n9cxpGbdwX0XwKFhlQMbG3rWA3YqQYWj1erKIPpgpfM64hwsdk9zZ QO1krgfULH4poPQFpl2+yVeEMXtsSou915jn/51rBelXeLq+cjuK5+B/JZUXPnNDoxOG3j3V VSZxkxLJ8RO1YamqZZbVP6jhDQ/bLcAI3EfjVbxhw9KWrh8MxTcmyJPn3QMMEp3wpVX9nSOQ tzG72Up/Py67VQe0x8fqmu7R4MmddSbyqgHrab/Nu+ak6g2RRn3QHXAQ7PQUq55BDtj85hd9 W2iBiROhkZ/R+Q14cJkWhzaThN1sZ1zsfBNW0Im8OVn/J8bQUaS0a/NhpXJWv6J1ttkX3S0c QUratRfX4D1viAwNgoS0Joq7xIQD+CfJTax7pPn9rT////hSqJYUoMXkEz5IcO+hptCH1HF3 qz77aA5njEBQrDRlslUBkCZ5P+QvZgJDy0C3xRGdg6ZVXEXJOQARAQABtCpIYW5uZXMgUmVp bmVja2UgKFN1U0UgTGFicykgPGhhcmVAc3VzZS5kZT6JAkEEEwECACsCGwMFCRLMAwAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheABQJOisquAhkBAAoJEGz4yi9OyKjPOHoQAJLeLvr6JNHx GPcHXaJLHQiinz2QP0/wtsT8+hE26dLzxb7hgxLafj9XlAXOG3FhGd+ySlQ5wSbbjdxNjgsq FIjqQ88/Lk1NfnqG5aUTPmhEF+PzkPogEV7Pm5Q17ap22VK623MPaltEba+ly6/pGOODbKBH ak3gqa7Gro5YCQzNU0QVtMpWyeGF7xQK76DY/atvAtuVPBJHER+RPIF7iv5J3/GFIfdrM+wS BubFVDOibgM7UBnpa7aohZ9RgPkzJpzECsbmbttxYaiv8+EOwark4VjvOne8dRaj50qeyJH6 HLpBXZDJH5ZcYJPMgunghSqghgfuUsd5fHmjFr3hDb5EoqAfgiRMSDom7wLZ9TGtT6viDldv hfWaIOD5UhpNYxfNgH6Y102gtMmN4o2P6g3UbZK1diH13s9DA5vI2mO2krGz2c5BOBmcctE5 iS+JWiCizOqia5Op+B/tUNye/YIXSC4oMR++Fgt30OEafB8twxydMAE3HmY+foawCpGq06yM vAguLzvm7f6wAPesDAO9vxRNC5y7JeN4Kytl561ciTICmBR80Pdgs/Obj2DwM6dvHquQbQrU Op4XtD3eGUW4qgD99DrMXqCcSXX/uay9kOG+fQBfK39jkPKZEuEV2QdpE4Pry36SUGfohSNq xXW+bMc6P+irTT39VWFUJMcSuQINBE6KyREBEACvEJggkGC42huFAqJcOcLqnjK83t4TVwEn JRisbY/VdeZIHTGtcGLqsALDzk+bEAcZapguzfp7cySzvuR6Hyq7hKEjEHAZmI/3IDc9nbdh EgdCiFatah0XZ/p4vp7KAelYqbv8YF/ORLylAdLh9rzLR6yHFqVaR4WL4pl4kEWwFhNSHLxe 55G56/dxBuoj4RrFoX3ynerXfbp4dH2KArPc0NfoamqebuGNfEQmDbtnCGE5zKcR0zvmXsRp qU7+caufueZyLwjTU+y5p34U4PlOO2Q7/bdaPEdXfpgvSpWk1o3H36LvkPV/PGGDCLzaNn04 BdiiiPEHwoIjCXOAcR+4+eqM4TSwVpTn6SNgbHLjAhCwCDyggK+3qEGJph+WNtNU7uFfscSP k4jqlxc8P+hn9IqaMWaeX9nBEaiKffR7OKjMdtFFnBRSXiW/kOKuuRdeDjL5gWJjY+IpdafP KhjvUFtfSwGdrDUh3SvB5knSixE3qbxbhbNxmqDVzyzMwunFANujyyVizS31DnWC6tKzANkC k15CyeFC6sFFu+WpRxvC6fzQTLI5CRGAB6FAxz8Hu5rpNNZHsbYs9Vfr/BJuSUfRI/12eOCL IvxRPpmMOlcI4WDW3EDkzqNAXn5Onx/b0rFGFpM4GmSPriEJdBb4M4pSD6fN6Y/Jrng/Bdwk SQARAQABiQIlBBgBAgAPBQJOiskRAhsMBQkSzAMAAAoJEGz4yi9OyKjPgEwQAIP/gy/Xqc1q OpzfFScswk3CEoZWSqHxn/fZasa4IzkwhTUmukuIvRew+BzwvrTxhHcz9qQ8hX7iDPTZBcUt ovWPxz+3XfbGqE+q0JunlIsP4N+K/I10nyoGdoFpMFMfDnAiMUiUatHRf9Wsif/nT6oRiPNJ T0EbbeSyIYe+ZOMFfZBVGPqBCbe8YMI+JiZeez8L9JtegxQ6O3EMQ//1eoPJ5mv5lWXLFQfx f4rAcKseM8DE6xs1+1AIsSIG6H+EE3tVm+GdCkBaVAZo2VMVapx9k8RMSlW7vlGEQsHtI0FT c1XNOCGjaP4ITYUiOpfkh+N0nUZVRTxWnJqVPGZ2Nt7xCk7eoJWTSMWmodFlsKSgfblXVfdM 9qoNScM3u0b9iYYuw/ijZ7VtYXFuQdh0XMM/V6zFrLnnhNmg0pnK6hO1LUgZlrxHwLZk5X8F uD/0MCbPmsYUMHPuJd5dSLUFTlejVXIbKTSAMd0tDSP5Ms8Ds84z5eHreiy1ijatqRFWFJRp ZtWlhGRERnDH17PUXDglsOA08HCls0PHx8itYsjYCAyETlxlLApXWdVl9YVwbQpQ+i693t/Y PGu8jotn0++P19d3JwXW8t6TVvBIQ1dRZHx1IxGLMn+CkDJMOmHAUMWTAXX2rf5tUjas8/v2 azzYF4VRJsdl+d0MCaSy8mUh Message-ID: <7bc94a9f-ec86-b343-0951-eba548c71b67@suse.de> Date: Wed, 11 Mar 2020 07:58:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20200311062228.GA13522@infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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. 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. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), GF: Felix Imendörffer