Re: [Qemu-devel] [PATCH] block/nvme: optimize the performance of nvme driver based on vfio-pci

[Fam Zheng <famz@redhat.com>]

On Thu, 11/01 18:38, Li Feng wrote:
> When the IO size is larger than 2 pages, we move the the pointer one by
> one in the pagelist, this is inefficient.
> 
> This is a simple benchmark result:
> 
> Before:
> $ qemu-io -c 'write 0 1G' nvme://0000:00:04.0/1
> 
> wrote 1073741824/1073741824 bytes at offset 0
> 1 GiB, 1 ops; 0:00:02.41 (424.504 MiB/sec and 0.4146 ops/sec)
> 
>  $ qemu-io -c 'read 0 1G' nvme://0000:00:04.0/1
> 
> read 1073741824/1073741824 bytes at offset 0
> 1 GiB, 1 ops; 0:00:02.03 (503.055 MiB/sec and 0.4913 ops/sec)
> 
> After:
> $ qemu-io -c 'write 0 1G' nvme://0000:00:04.0/1
> 
> wrote 1073741824/1073741824 bytes at offset 0
> 1 GiB, 1 ops; 0:00:02.17 (471.517 MiB/sec and 0.4605 ops/sec)
> 
>  $ qemu-io -c 'read 0 1G' nvme://0000:00:04.0/1                                                                                                                                                                                                                                                                      1 ↵
> 
> read 1073741824/1073741824 bytes at offset 0
> 1 GiB, 1 ops; 0:00:01.94 (526.770 MiB/sec and 0.5144 ops/sec)
> 
> Signed-off-by: Li Feng <lifeng1519@gmail.com>
> ---
>  block/nvme.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/block/nvme.c b/block/nvme.c
> index 29294038fc..982097b5b1 100644
> --- a/block/nvme.c
> +++ b/block/nvme.c
> @@ -837,7 +837,7 @@ try_map:
>          }
>  
>          for (j = 0; j < qiov->iov[i].iov_len / s->page_size; j++) {
> -            pagelist[entries++] = iova + j * s->page_size;
> +            pagelist[entries++] = cpu_to_le64(iova + j * s->page_size);
>          }
>          trace_nvme_cmd_map_qiov_iov(s, i, qiov->iov[i].iov_base,
>                                      qiov->iov[i].iov_len / s->page_size);
> @@ -850,20 +850,16 @@ try_map:
>      case 0:
>          abort();
>      case 1:
> -        cmd->prp1 = cpu_to_le64(pagelist[0]);
> +        cmd->prp1 = pagelist[0];
>          cmd->prp2 = 0;
>          break;
>      case 2:
> -        cmd->prp1 = cpu_to_le64(pagelist[0]);
> -        cmd->prp2 = cpu_to_le64(pagelist[1]);;
> +        cmd->prp1 = pagelist[0];
> +        cmd->prp2 = pagelist[1];
>          break;
>      default:
> -        cmd->prp1 = cpu_to_le64(pagelist[0]);
> -        cmd->prp2 = cpu_to_le64(req->prp_list_iova);
> -        for (i = 0; i < entries - 1; ++i) {
> -            pagelist[i] = cpu_to_le64(pagelist[i + 1]);
> -        }
> -        pagelist[entries - 1] = 0;
> +        cmd->prp1 = pagelist[0];
> +        cmd->prp2 = cpu_to_le64(req->prp_list_iova + sizeof(uint64_t));
>          break;
>      }
>      trace_nvme_cmd_map_qiov(s, cmd, req, qiov, entries);
> -- 
> 2.11.0
> 

Nice! Thanks. I've queued the patch.

Fam