Re: [Qemu-devel] [PATCH V2] qemu-img: make convert async

[Eric Blake <eblake@redhat.com>]

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On 02/27/2017 05:03 AM, Peter Lieven wrote:
> the convert process is currently completely implemented with sync operations.
> That means it reads one buffer and then writes it. No parallelism and each sync
> request takes as long as it takes until it is completed.
> 

> 
> This patches introduces 2 new cmdline parameters. The -m parameter to specify
> the number of coroutines running in parallel (defaults to 8). And the -W paremeter to

s/paremeter/parameter/

> allow qemu-img to write to the target out of order rather than sequential. This improves
> performance as the writes do not have to wait for each other to complete.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---

> @@ -1798,7 +1908,7 @@ static int img_convert(int argc, char **argv)
>              {"image-opts", no_argument, 0, OPTION_IMAGE_OPTS},
>              {0, 0, 0, 0}
>          };
> -        c = getopt_long(argc, argv, "hf:O:B:ce6o:s:l:S:pt:T:qn",
> +        c = getopt_long(argc, argv, "hf:O:B:ce6o:s:l:S:pt:T:qnm:W",
>                          long_options, NULL);
>          if (c == -1) {
>              break;
> @@ -1890,6 +2000,18 @@ static int img_convert(int argc, char **argv)
>          case 'n':
>              skip_create = 1;
>              break;
> +        case 'm':
> +            num_coroutines = atoi(optarg);

atoi() should be avoided. It has no error checking, so it treats '-m 1'
and '-m 1k' identically.  You are a bit justified in that '-m junk' gets
treated like '-m 0' and rejected, but it's still a poor error message in
that case.

> +            if (num_coroutines < 1 || num_coroutines > MAX_COROUTINES) {
> +                error_report("Allowed number of coroutines is between 1 and %d",
> +                             MAX_COROUTINES);

> +++ b/qemu-img.texi
> @@ -137,6 +137,12 @@ Parameters to convert subcommand:
>  
>  @item -n
>  Skip the creation of the target volume
> +@item -m
> +Number of parallel coroutines for the convert process
> +@item -W
> +Allow to write out of order to the destination. This is option improves performance,

Grammar suggestion:

Allow out-of-order writes to the destination.  This option ...

> +but is only recommened for preallocated devices like host devices or other

s/recommened/recommended/

> +raw block devices.
>  @end table
>  


-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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