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@xxxxxx>
> ---
> 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@xxxxxxx>
