nvme-pci: optimize mapping single segment requests using SGLs

If the controller supports SGLs we can take another short cut for single
segment request, given that we can always map those without another
indirection structure, and thus don't need to create a scatterlist
structure.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 59731264b052c3e90a20b5d94d3fd8b369f566fe..82aa5cb21828b058d873fd53fc8ae4ee3294624c 100644 (file)
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -819,6 +819,23 @@ static blk_status_t nvme_setup_prp_simple(struct nvme_dev *dev,
        return 0;
 }
 
+static blk_status_t nvme_setup_sgl_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);
+
+       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.sgl.addr = cpu_to_le64(iod->first_dma);
+       cmnd->dptr.sgl.length = cpu_to_le32(iod->dma_len);
+       cmnd->dptr.sgl.type = NVME_SGL_FMT_DATA_DESC << 4;
+       return 0;
+}
+
 static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
                struct nvme_command *cmnd)
 {
@@ -836,6 +853,11 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
                        if (bv.bv_offset + bv.bv_len <= dev->ctrl.page_size * 2)
                                return nvme_setup_prp_simple(dev, req,
                                                             &cmnd->rw, &bv);
+
+                       if (iod->nvmeq->qid &&
+                           dev->ctrl.sgls & ((1 << 0) | (1 << 1)))
+                               return nvme_setup_sgl_simple(dev, req,
+                                                            &cmnd->rw, &bv);
                }
        }