[PATCH] NVMe: Avoid caculate cq head doorbel in nvme_process_cq()

[h.huangqiang@huawei.com (Qiang Huang)]

Hi haiyan,

You overlooked zefan's inline comments.

And the pattern of the patch looks odd, you'd better use
# git format-patch -1 -s
to create patches, and get a new email client like thunderbird.

You can get more information from Documentation/SubmittingPatches.

On 2013/9/2 14:36, Huhaiyan (haiyan) wrote:
> We use 2 pointers, one for sq tail doorbell, the other for cq head doorbell in struct nvme_queue, to avoid calculate cq head doorbell in nvme_process_cq().
> 
> This change can reduce latency for the admin/io command.
> 
> 
> 
> Signed-off-by: Haiyan Hu <huhaiyan at huawei.com >
> 
> 
> 
> ---
> 
> drivers/block/nvme-core.c |   19 +++++++++++--------
> 
> 1 files changed, 11 insertions(+), 8 deletions(-)
> 
> 
> 
> diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c index 7de80bb..80cf07c 100644
> 
> --- a/drivers/block/nvme-core.c
> 
> +++ b/drivers/block/nvme-core.c
> 
> @@ -74,7 +74,8 @@ struct nvme_queue {
> 
>        wait_queue_head_t sq_full;
> 
>        wait_queue_t sq_cong_wait;
> 
>        struct bio_list sq_cong;
> 
> -        u32 __iomem *q_db;
> 
> +       u32 __iomem *sq_tail_db;
> 
> +       u32 __iomem *cq_head_db;
> 
>        u16 q_depth;
> 
>        u16 cq_vector;
> 
>        u16 sq_head;
> 
> @@ -252,7 +253,7 @@ static int nvme_submit_cmd(struct nvme_queue *nvmeq, struct nvme_command *cmd)
> 
>        memcpy(&nvmeq->sq_cmds[tail], cmd, sizeof(*cmd));
> 
>        if (++tail == nvmeq->q_depth)
> 
>                 tail = 0;
> 
> -        writel(tail, nvmeq->q_db);
> 
> +       writel(tail, nvmeq->sq_tail_db);
> 
>        nvmeq->sq_tail = tail;
> 
>        spin_unlock_irqrestore(&nvmeq->q_lock, flags);
> 
> @@ -618,7 +619,7 @@ static int nvme_submit_discard(struct nvme_queue *nvmeq, struct nvme_ns *ns,
> 
>         if (++nvmeq->sq_tail == nvmeq->q_depth)
> 
>                 nvmeq->sq_tail = 0;
> 
> -        writel(nvmeq->sq_tail, nvmeq->q_db);
> 
> +       writel(nvmeq->sq_tail, nvmeq->sq_tail_db);
> 
>         return 0;
> 
> }
> 
> @@ -635,7 +636,7 @@ static int nvme_submit_flush(struct nvme_queue *nvmeq, struct nvme_ns *ns,
> 
>         if (++nvmeq->sq_tail == nvmeq->q_depth)
> 
>                 nvmeq->sq_tail = 0;
> 
> -        writel(nvmeq->sq_tail, nvmeq->q_db);
> 
> +       writel(nvmeq->sq_tail, nvmeq->sq_tail_db);
> 
>         return 0;
> 
> }
> 
> @@ -728,7 +729,7 @@ static int nvme_submit_bio_queue(struct nvme_queue *nvmeq, struct nvme_ns *ns,
> 
>        nvme_start_io_acct(bio);
> 
>        if (++nvmeq->sq_tail == nvmeq->q_depth)
> 
>                 nvmeq->sq_tail = 0;
> 
> -        writel(nvmeq->sq_tail, nvmeq->q_db);
> 
> +       writel(nvmeq->sq_tail, nvmeq->sq_tail_db);
> 
>         return 0;
> 
> @@ -772,7 +773,7 @@ static int nvme_process_cq(struct nvme_queue *nvmeq)
> 
>        if (head == nvmeq->cq_head && phase == nvmeq->cq_phase)
> 
>                 return 0;
> 
> -        writel(head, nvmeq->q_db + (1 << nvmeq->dev->db_stride));
> 
> +       writel(head, nvmeq->cq_head_db);
> 
>        nvmeq->cq_head = head;
> 
>        nvmeq->cq_phase = phase;
> 
> @@ -1084,7 +1085,8 @@ static struct nvme_queue *nvme_alloc_queue(struct nvme_dev *dev, int qid,
> 
>        init_waitqueue_head(&nvmeq->sq_full);
> 
>        init_waitqueue_entry(&nvmeq->sq_cong_wait, nvme_thread);
> 
>        bio_list_init(&nvmeq->sq_cong);
> 
> -        nvmeq->q_db = &dev->dbs[qid << (dev->db_stride + 1)];
> 
> +       nvmeq->sq_tail_db = &dev->dbs[qid << (dev->db_stride + 1)];
> 
> +       nvmeq->cq_head_db = nvmeq->sq_tail_db + (1 << dev->db_stride);
> 
>        nvmeq->q_depth = depth;
> 
>        nvmeq->cq_vector = vector;
> 
> @@ -1690,7 +1692,8 @@ static int nvme_setup_io_queues(struct nvme_dev *dev)
> 
>                 iounmap(dev->bar);
> 
>                 dev->bar = ioremap(pci_resource_start(pdev, 0), db_bar_size);
> 
>                 dev->dbs = ((void __iomem *)dev->bar) + 4096;
> 
> -                 dev->queues[0]->q_db = dev->dbs;
> 
> +                dev->queues[0]->sq_tail_db = dev->dbs;
> 
> +               dev->queues[0]->cq_head_db = dev->dbs + (1 << dev->db_stride);
> 
>        }
> 
>         vecs = nr_io_queues;
> 
> --
> 
> 1.7.6
> 
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