[PATCH v5 RFC] nvme: improve performance for virtual NVMe devices

[hch@infradead.org (Christoph Hellwig)]

> +#define SQ_IDX(qid, stride)	((qid) * 2 * (stride))
> +#define CQ_IDX(qid, stride)	(((qid) * 2 + 1) * (stride))

Please use inline functions for these.

> +	struct {
> +		u32 *dbs;
> +		u32 *eis;
> +		dma_addr_t dbs_dma_addr;
> +		dma_addr_t eis_dma_addr;
> +	} dbbuf;

No need for a struct here, also please keep the field and its dma_addr_t
together.

> +	struct {
> +		u32 *sq_db;
> +		u32 *cq_db;
> +		u32 *sq_ei;
> +		u32 *cq_ei;
> +	} dbbuf;

No need for the struct here either.

> +
> +static int nvme_dbbuf_dma_alloc(struct nvme_dev *dev)
> +{
> +	unsigned int mem_size = nvme_dbbuf_size(dev->db_stride);
> +
> +	dev->dbbuf.dbs = dma_alloc_coherent(dev->dev, mem_size,
> +					    &dev->dbbuf.dbs_dma_addr,
> +					    GFP_KERNEL);
> +	if (!dev->dbbuf.dbs)
> +		return -ENOMEM;
> +	dev->dbbuf.eis = dma_alloc_coherent(dev->dev, mem_size,
> +					    &dev->dbbuf.eis_dma_addr,
> +					    GFP_KERNEL);
> +	if (!dev->dbbuf.eis) {
> +		dma_free_coherent(dev->dev, mem_size,
> +				  dev->dbbuf.dbs, dev->dbbuf.dbs_dma_addr);
> +		dev->dbbuf.dbs = NULL;
> +		return -ENOMEM;
> +	}
> +
> +	return 0;

Please use normal kernel-style goto unwinding.

> +static void nvme_dbbuf_set(struct nvme_dev *dev)
> +{
> +	struct nvme_command c;
> +
> +	if (!dev->dbbuf.dbs)
> +		return;
> +
> +	memset(&c, 0, sizeof(c));
> +	c.dbbuf.opcode = nvme_admin_dbbuf;
> +	c.dbbuf.prp1 = cpu_to_le64(dev->dbbuf.dbs_dma_addr);
> +	c.dbbuf.prp2 = cpu_to_le64(dev->dbbuf.eis_dma_addr);
> +
> +	if (nvme_submit_sync_cmd(dev->ctrl.admin_q, &c, NULL, 0))
> +		/* Free memory and continue on */
> +		nvme_dbbuf_dma_free(dev);

At least log a warning.

> +static inline int nvme_dbbuf_need_event(u16 event_idx, u16 new_idx, u16 old)
> +{
> +	/* Borrowed from vring_need_event */

I don't think this comment matters.

> +static void nvme_write_doorbell(u16 value,
> +				u32 __iomem *db,
> +				u32 *dbbuf_db,
> +				volatile u32 *dbbuf_ei)
> +{

Very odd formatting.  Why not:

static void nvme_write_doorbell(u16 value, u32 __iomem *db, u32 *dbbuf_db,
		volatile u32 *dbbuf_ei)

?

> +	u16 old_value;
> +
> +	if (!dbbuf_db) {
> +		writel(value, db);
> +		return;
> +	}

I'd prefer to keep this in the ultimate callers to make the flow
easier to read.

> +static inline void nvme_write_doorbell_cq(struct nvme_queue *nvmeq, u16 value)
> +{
> +	nvme_write_doorbell(value, nvmeq->q_db + nvmeq->dev->db_stride,
> +			    nvmeq->dbbuf.cq_db, nvmeq->dbbuf.cq_ei);
> +}
> +
> +static inline void nvme_write_doorbell_sq(struct nvme_queue *nvmeq, u16 value)
> +{
> +	nvme_write_doorbell(value, nvmeq->q_db,
> +			    nvmeq->dbbuf.sq_db, nvmeq->dbbuf.sq_ei);
>  }

I'd skip these wrappers entirely.

> +	if (dev->ctrl.oacs & NVME_CTRL_OACS_DBBUF_SUPP) {
> +		result = nvme_dbbuf_dma_alloc(dev);
> +		if (result)
> +			goto out;
> +	}

Should we really fail the init here or just print a warning?