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Re: [Qemu-devel] [RFC PATCH v2 10/12] mc: expose tunable parameter for c
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [RFC PATCH v2 10/12] mc: expose tunable parameter for checkpointing frequency |
Date: |
Tue, 11 Mar 2014 15:49:49 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 |
On 02/18/2014 01:50 AM, address@hidden wrote:
> From: "Michael R. Hines" <address@hidden>
>
> This exposes a QMP command that allows the management software
> or policy to control the frequency of micro-checkpointing.
>
> Signed-off-by: Michael R. Hines <address@hidden>
> ---
> hmp-commands.hx | 16 +++++++++++++++-
> hmp.c | 6 ++++++
> hmp.h | 1 +
> qapi-schema.json | 13 +++++++++++++
> qmp-commands.hx | 23 +++++++++++++++++++++++
> 5 files changed, 58 insertions(+), 1 deletion(-)
>
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index f3fc514..2066c76 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -888,7 +888,7 @@ ETEXI
> "\n\t\t\t -b for migration without shared storage with"
> " full copy of disk\n\t\t\t -i for migration without "
> "shared storage with incremental copy of disk "
> - "(base image shared between src and destination)",
> + "(base image shared between src and destination)",
Spurious hunk. Oh, I see - you managed to take TAB damage and make it
worse with a space-TAB (I guess this file isn't tab-clean, like the
.json file is). Eww.
> .mhandler.cmd = hmp_migrate,
> },
>
> @@ -965,6 +965,20 @@ Set maximum tolerated downtime (in seconds) for
> migration.
> ETEXI
>
> {
> + .name = "migrate-set-mc-delay",
We're building up a LOT of migrate- tunable commands. Maybe it's time
to think about building a more generic migrate-set-parameter, which
takes both the name of the parameter to set and its value, so that a
single command serves all parameters, instead of needing a proliferation
of commands. Of course, for that to be useful, we also need a way to
introspect which parameters can be tuned; whereas with the current
approach of one command per parameter (well, 2 for set vs. get) the
introspection is based on whether the command exists.
> +++ b/qapi-schema.json
> @@ -2160,6 +2160,19 @@
> { 'command': 'migrate_set_downtime', 'data': {'value': 'number'} }
>
> ##
> +# @migrate-set-mc-delay
> +#
> +# Set delay (in milliseconds) between micro checkpoints.
> +#
> +# @value: maximum delay in milliseconds
> +#
> +# Returns: nothing on success
> +#
> +# Since: 2.x
> +##
> +{ 'command': 'migrate-set-mc-delay', 'data': {'value': 'int'} }
> +
> +##
I hate write-only interfaces. If I can set the parameter, I _also_ need
a way to query the current value of the parameter. Either an existing
migration statistics output should be modified to include this new
information, or you need to add a counterpart migrate-get-mc-delay command.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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