Re: [PATCH 1/2] nvme: support fused nvme requests

[James Smart <james.smart@broadcom.com>]

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On 1/5/2021 2:49 PM, klayph@gmail.com wrote:
> From

>   
>   /*
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 3be352403839..c24729e100bc 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -491,6 +491,30 @@ static inline void nvme_write_sq_db(struct nvme_queue *nvmeq, bool write_sq)
>   	nvmeq->last_sq_tail = nvmeq->sq_tail;
>   }
>   
> +/**
> + * nvme_submit_cmd2() - Copy fused commands into a queue and ring the doorbell
> + * @nvmeq: The queue to use
> + * @cmd: The first command to send
> + * @cmd2: the second command to send
> + * @write_sq: whether to write to the SQ doorbell
> + */
> +static void nvme_submit_cmd2(struct nvme_queue *nvmeq, struct nvme_command *cmd,
> +			     struct nvme_command *cmd2, bool write_sq)
> +{
> +	spin_lock(&nvmeq->sq_lock);
> +	memcpy(nvmeq->sq_cmds + (nvmeq->sq_tail << nvmeq->sqes),
> +		cmd, sizeof(*cmd));
> +	if (++nvmeq->sq_tail == nvmeq->q_depth)
> +		nvmeq->sq_tail = 0;
> +	memcpy(nvmeq->sq_cmds + (nvmeq->sq_tail << nvmeq->sqes),
> +		cmd2, sizeof(*cmd2));
> +	if (++nvmeq->sq_tail == nvmeq->q_depth)
> +		nvmeq->sq_tail = 0;
> +	nvme_write_sq_db(nvmeq, write_sq);
> +	spin_unlock(&nvmeq->sq_lock);
> +}
> +
> +
>   /**
>    * nvme_submit_cmd() - Copy a command into a queue and ring the doorbell
>    * @nvmeq: The queue to use
> @@ -918,7 +942,13 @@ static blk_status_t nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
>   	}
>   
>   	blk_mq_start_request(req);
> -	nvme_submit_cmd(nvmeq, &cmnd, bd->last);
> +
> +	if (cmnd.common.flags & NVME_CMD_FUSE_FIRST)
> +		memcpy(&nvme_req(req)->nrq2->cmnd, &cmnd, sizeof(cmnd));
> +	else if (cmnd.common.flags & NVME_CMD_FUSE_SECOND)
> +		nvme_submit_cmd2(nvmeq, &nvme_req(req)->cmnd, &cmnd, bd->last);
> +	else
> +		nvme_submit_cmd(nvmeq, &cmnd, bd->last);
>   	return BLK_STS_OK;
>   out_unmap_data:
>   	nvme_unmap_data(dev, req);

I think Keith caught the most concerning issue. I've been thinking of 
others but they mostly seem to work.  I assume recopies of the first 
fused cmd to the data structure don't hurt.  I would expect there to be 
a couple of other odd issues if the two requests start working 
independently.

This is the pci transport only. You should either put something in to 
not allow the ioctl on a non-pci transport, or add the support (or 
rejection) to the fabric transports as well.

-- james




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