From mboxrd@z Thu Jan 1 00:00:00 1970 From: keith.busch@intel.com (Keith Busch) Date: Tue, 22 Oct 2013 13:52:25 -0600 (MDT) Subject: [PATCH 3/3] NVMe: Convert to blk-mq In-Reply-To: <5266CA29.2020308@bjorling.me> References: <1382102062-22270-1-git-send-email-m@bjorling.me> <1382102062-22270-4-git-send-email-m@bjorling.me> <526186AE.3080006@bjorling.me> <5266CA29.2020308@bjorling.me> Message-ID: On Tue, 22 Oct 2013, Matias Bjorling wrote: > Den 22-10-2013 18:55, Keith Busch skrev: >> On Fri, 18 Oct 2013, Matias Bj?rling wrote: >>> On 10/18/2013 05:13 PM, Keith Busch wrote: >>>> On Fri, 18 Oct 2013, Matias Bjorling wrote: >>>>> The nvme driver implements itself as a bio-based driver. This primarily >>>>> because of high lock congestion for high-performance nvm devices. To >>>>> remove the congestion within the traditional block layer, a multi-queue >>>>> block layer is being implemented. >> >>>>> - result = nvme_map_bio(nvmeq, iod, bio, dma_dir, psegs); >>>>> - if (result <= 0) >>>>> + if (nvme_map_rq(nvmeq, iod, rq, dma_dir)) >>>>> goto free_cmdid; >>>>> - length = result; >>>>> >>>>> - cmnd->rw.command_id = cmdid; >>>>> + length = blk_rq_bytes(rq); >>>>> + >>>>> + cmnd->rw.command_id = rq->tag; >>>> >>>> The command ids have to be unique on a submission queue. Since each >>>> namespace's blk-mq has its own 'tags' used as command ids here but share >>>> submission queues, what's stopping the tags for commands sent to >>>> namespace >>>> 1 from clashing with tags for namespace 2? >>>> >>>> I think this would work better if one blk-mq was created per device >>>> rather than namespace. It would fix the tag problem above and save a >>>> lot of memory potentially wasted on millions of requests allocated that >>>> can't be used. >>> >>> You're right. I didn't see the connection. In v3 I'll push struct >>> request_queue to nvme_dev and map the queues appropriately. It will also >>> fix the command id issues. >> >> Just anticipating a possible issue with the suggestion. Will this separate >> the logical block size from the request_queue? Each namespace can have >> a different format, so the block size and request_queue can't be tied >> together like it currently is for this to work. > > If only a couple of different logical sizes are to be expected (1-4), we can > keep a list of already initialized request queues, and use the one that match > an already initialized? The spec allows a namespace to have up to 16 different block formats and they need not be the same 16 as another namespace on the same device. >>From a practical standpoint, I don't think devices will support more than a few formats, but even if you kept it to that many request queues, you just get back to conflicting command id tags and some wasted memory. > > Axboe, do you know of a better solution?