Re: [Qemu-devel] [PATCHv2 1.8 6/9] qemu-img: dynamically adjust iobuffer size during convert

[Paolo Bonzini]

Il 26/11/2013 09:56, Peter Lieven ha scritto:
> since the convert process is basically a sync operation it might
> be benificial in some case to change the hardcoded I/O buffer
> size to a greater value.
> 
> This patch increases the I/O buffer size if the output
> driver advertises an optimal transfer length or discard alignment
> that is greater than the default buffer size of 2M.
> 
> Signed-off-by: Peter Lieven <address@hidden>
> ---
>  qemu-img.c |   18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/qemu-img.c b/qemu-img.c
> index e2d1a0a..b076d44 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1135,6 +1135,7 @@ static int img_convert(int argc, char **argv)
>              sector_num_next_status = 0;
>      uint64_t bs_sectors;
>      uint8_t * buf = NULL;
> +    size_t bufsectors = IO_BUF_SIZE / BDRV_SECTOR_SIZE;
>      const uint8_t *buf1;
>      BlockDriverInfo bdi;
>      QEMUOptionParameter *param = NULL, *create_options = NULL;
> @@ -1371,7 +1372,16 @@ static int img_convert(int argc, char **argv)
>      bs_i = 0;
>      bs_offset = 0;
>      bdrv_get_geometry(bs[0], &bs_sectors);
> -    buf = qemu_blockalign(out_bs, IO_BUF_SIZE);
> +
> +    /* increase bufsectors from the default 4096 (2M) if opt_transfer_length
> +     * or discard_alignment of the out_bs is greater. Limit to 32768 (16MB)
> +     * as maximum. */
> +    bufsectors = MIN(32768,
> +                     MAX(bufsectors, MAX(out_bs->bl.opt_transfer_length,
> +                                         out_bs->bl.discard_alignment))
> +                    );
> +
> +    buf = qemu_blockalign(out_bs, bufsectors * BDRV_SECTOR_SIZE);
>  
>      if (skip_create) {
>          int64_t output_length = bdrv_getlength(out_bs);
> @@ -1394,7 +1404,7 @@ static int img_convert(int argc, char **argv)
>              goto out;
>          }
>          cluster_size = bdi.cluster_size;
> -        if (cluster_size <= 0 || cluster_size > IO_BUF_SIZE) {
> +        if (cluster_size <= 0 || cluster_size > bufsectors * 
> BDRV_SECTOR_SIZE) {
>              error_report("invalid cluster size");
>              ret = -1;
>              goto out;
> @@ -1531,8 +1541,8 @@ static int img_convert(int argc, char **argv)
>                  sector_num_next_status = sector_num + n1;
>              }
>  
> -            if (nb_sectors >= (IO_BUF_SIZE / 512)) {
> -                n = (IO_BUF_SIZE / 512);
> +            if (nb_sectors >= bufsectors) {
> +                n = bufsectors;
>              } else {
>                  n = nb_sectors;
>              }
> 

Reviewed-by: Paolo Bonzini <address@hidden>