Re: [PATCH v2 00/16] block atomic writes

Keith Busch
2023-12-18T22:50:20Z

On Thu, Dec 14, 2023 at 03:37:09PM +0100, Christoph Hellwig wrote:
> On Wed, Dec 13, 2023 at 04:27:35PM +0000, John Garry wrote:
> >>> Are there any patches yet for the change to always use SGLs for transfers
> >>> larger than a single PRP?
> >> No.
>
> Here is the WIP version. With that you'd need to make atomic writes
> conditional on !ctrl->need_virt_boundary.

This looks pretty good as-is!

> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 8ebdfd623e0f78..e04faffd6551fe 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -1889,7 +1889,8 @@ static void nvme_set_queue_limits(struct nvme_ctrl *ctrl,
> blk_queue_max_hw_sectors(q, ctrl->max_hw_sectors);
> blk_queue_max_segments(q, min_t(u32, max_segments, USHRT_MAX));
> }
> - blk_queue_virt_boundary(q, NVME_CTRL_PAGE_SIZE - 1);
> + if (q == ctrl->admin_q || ctrl->need_virt_boundary)
> + blk_queue_virt_boundary(q, NVME_CTRL_PAGE_SIZE - 1);
> blk_queue_dma_alignment(q, 3);
> blk_queue_write_cache(q, vwc, vwc);
> }
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index e7411dac00f725..aa98794a3ec53d 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -262,6 +262,7 @@ enum nvme_ctrl_flags {
> struct nvme_ctrl {
> bool comp_seen;
> bool identified;
> + bool need_virt_boundary;
> enum nvme_ctrl_state state;
> spinlock_t lock;
> struct mutex scan_lock;
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 61af7ff1a9d6ba..a8d273b475cb40 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -60,8 +60,7 @@ MODULE_PARM_DESC(max_host_mem_size_mb,
> static unsigned int sgl_threshold = SZ_32K;
> module_param(sgl_threshold, uint, 0644);
> MODULE_PARM_DESC(sgl_threshold,
> - "Use SGLs when average request segment size is larger or equal to "
> - "this size. Use 0 to disable SGLs.");
> + "Use SGLs when > 0. Use 0 to disable SGLs.");
>
> #define NVME_PCI_MIN_QUEUE_SIZE 2
> #define NVME_PCI_MAX_QUEUE_SIZE 4095
> @@ -504,23 +503,6 @@ static void nvme_commit_rqs(struct blk_mq_hw_ctx *hctx)
> spin_unlock(&nvmeq->sq_lock);
> }
>
> -static inline bool nvme_pci_use_sgls(struct nvme_dev *dev, struct request *req,
> - int nseg)
> -{
> - struct nvme_queue *nvmeq = req->mq_hctx->driver_data;
> - unsigned int avg_seg_size;
> -
> - avg_seg_size = DIV_ROUND_UP(blk_rq_payload_bytes(req), nseg);
> -
> - if (!nvme_ctrl_sgl_supported(&dev->ctrl))
> - return false;
> - if (!nvmeq->qid)
> - return false;
> - if (!sgl_threshold || avg_seg_size < sgl_threshold)
> - return false;
> - return true;
> -}
> -
> static void nvme_free_prps(struct nvme_dev *dev, struct request *req)
> {
> const int last_prp = NVME_CTRL_PAGE_SIZE / sizeof(__le64) - 1;
> @@ -769,12 +751,14 @@ static blk_status_t nvme_setup_sgl_simple(struct nvme_dev *dev,
> static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
> struct nvme_command *cmnd)
> {
> + struct nvme_queue *nvmeq = req->mq_hctx->driver_data;
> struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> + bool sgl_supported = nvme_ctrl_sgl_supported(&dev->ctrl) &&
> + nvmeq->qid && sgl_threshold;
> blk_status_t ret = BLK_STS_RESOURCE;
> int rc;
>
> if (blk_rq_nr_phys_segments(req) == 1) {
> - struct nvme_queue *nvmeq = req->mq_hctx->driver_data;
> struct bio_vec bv = req_bvec(req);
>
> if (!is_pci_p2pdma_page(bv.bv_page)) {
> @@ -782,8 +766,7 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
> return nvme_setup_prp_simple(dev, req,
> &cmnd->rw, &bv);
>
> - if (nvmeq->qid && sgl_threshold &&
> - nvme_ctrl_sgl_supported(&dev->ctrl))
> + if (sgl_supported)
> return nvme_setup_sgl_simple(dev, req,
> &cmnd->rw, &bv);
> }
> @@ -806,7 +789,7 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
> goto out_free_sg;
> }
>
> - if (nvme_pci_use_sgls(dev, req, iod->sgt.nents))
> + if (sgl_supported)
> ret = nvme_pci_setup_sgls(dev, req, &cmnd->rw);
> else
> ret = nvme_pci_setup_prps(dev, req, &cmnd->rw);
> @@ -3036,6 +3019,8 @@ static int nvme_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> result = nvme_init_ctrl_finish(&dev->ctrl, false);
> if (result)
> goto out_disable;
> + if (!nvme_ctrl_sgl_supported(&dev->ctrl))
> + dev->ctrl.need_virt_boundary = true;
>
> nvme_dbbuf_dma_alloc(dev);
>
> diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
> index 81e2621169e5d3..416a9fbcccfc74 100644
> --- a/drivers/nvme/host/rdma.c
> +++ b/drivers/nvme/host/rdma.c
> @@ -838,6 +838,7 @@ static int nvme_rdma_configure_admin_queue(struct nvme_rdma_ctrl *ctrl,
> error = nvme_init_ctrl_finish(&ctrl->ctrl, false);
> if (error)
> goto out_quiesce_queue;
> + ctrl->ctrl.need_virt_boundary = true;
>
> return 0;
>