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Re: [Qemu-block] [PATCH V2] qemu-img: make convert async
From: |
Eric Blake |
Subject: |
Re: [Qemu-block] [PATCH V2] qemu-img: make convert async |
Date: |
Mon, 27 Feb 2017 15:09:57 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 |
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 <address@hidden>
> ---
> @@ -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
> address@hidden -m
> +Number of parallel coroutines for the convert process
> address@hidden -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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