From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chaitanya.Kulkarni@wdc.com (Chaitanya Kulkarni)
Date: Mon, 25 Mar 2019 05:36:18 +0000
Subject: [PATCH 13/15] nvme-pci: optimize mapping of small single segment
 requests
References: <20190321231037.25104-1-hch@lst.de>
 <20190321231037.25104-14-hch@lst.de>
Message-ID: <SN6PR04MB45278E0897CCD5C2069E745B865E0@SN6PR04MB4527.namprd04.prod.outlook.com>

On 3/21/19 4:12 PM, Christoph Hellwig wrote:
> If a request is single segment and fits into one or two PRP entries we
> do not have to create a scatterlist for it, but can just map the bio_vec
> directly.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>   drivers/nvme/host/pci.c | 45 ++++++++++++++++++++++++++++++++++++-----
>   1 file changed, 40 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index c6047935e825..47fc4d653961 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -221,6 +221,7 @@ struct nvme_iod {
>   	int npages;		/* In the PRP list. 0 means small pool in use */
>   	int nents;		/* Used in scatterlist */
>   	dma_addr_t first_dma;
> +	unsigned int dma_len;	/* length of single DMA segment mapping */
>   	dma_addr_t meta_dma;
>   	struct scatterlist *sg;
>   };
> @@ -576,13 +577,18 @@ static void nvme_unmap_data(struct nvme_dev *dev, struct request *req)
>   	dma_addr_t dma_addr = iod->first_dma, next_dma_addr;
>   	int i;
>   
> -	if (iod->nents) {
> -		/* P2PDMA requests do not need to be unmapped */
> -		if (!is_pci_p2pdma_page(sg_page(iod->sg)))
> -			dma_unmap_sg(dev->dev, iod->sg, iod->nents, dma_dir);
> -
> +	if (iod->dma_len) {
> +		dma_unmap_page(dev->dev, dma_addr, iod->dma_len, dma_dir);
> +		return;
>   	}
>   
> +	WARN_ON_ONCE(!iod->nents);
> +
> +	/* P2PDMA requests do not need to be unmapped */
> +	if (!is_pci_p2pdma_page(sg_page(iod->sg)))
> +		dma_unmap_sg(dev->dev, iod->sg, iod->nents, rq_dma_dir(req));
> +
> +
>   	if (iod->npages == 0)
>   		dma_pool_free(dev->prp_small_pool, nvme_pci_iod_list(req)[0],
>   			dma_addr);
> @@ -795,6 +801,24 @@ static blk_status_t nvme_pci_setup_sgls(struct nvme_dev *dev,
>   	return BLK_STS_OK;
>   }
>   
> +static blk_status_t nvme_setup_prp_simple(struct nvme_dev *dev,
> +		struct request *req, struct nvme_rw_command *cmnd,
> +		struct bio_vec *bv)
> +{
> +	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> +	unsigned int first_prp_len = dev->ctrl.page_size - bv->bv_offset;
> +
> +	iod->first_dma = dma_map_bvec(dev->dev, bv, rq_dma_dir(req), 0);
> +	if (dma_mapping_error(dev->dev, iod->first_dma))
> +		return BLK_STS_RESOURCE;
> +	iod->dma_len = bv->bv_len;
> +
> +	cmnd->dptr.prp1 = cpu_to_le64(iod->first_dma);
> +	if (bv->bv_len > first_prp_len)
> +		cmnd->dptr.prp2 = cpu_to_le64(iod->first_dma + first_prp_len);
> +	return 0;
> +}
> +
>   static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
>   		struct nvme_command *cmnd)
>   {
> @@ -805,6 +829,17 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
>   	blk_status_t ret = BLK_STS_IOERR;
>   	int nr_mapped;
>   
> +	if (blk_rq_nr_phys_segments(req) == 1) {
> +		struct bio_vec bv = req_bvec(req);
> +
> +		if (!is_pci_p2pdma_page(bv.bv_page)) {
> +			if (bv.bv_offset + bv.bv_len <= dev->ctrl.page_size * 2)
> +				return nvme_setup_prp_simple(dev, req,
> +							     &cmnd->rw, &bv);
> +		}
> +	}
> +
> +	iod->dma_len = 0;
>   	iod->sg = mempool_alloc(dev->iod_mempool, GFP_ATOMIC);
>   	if (!iod->sg)
>   		return BLK_STS_RESOURCE;
> 
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni at wdc.com>