Re: [Qemu-devel] [PATCH v12 1/6] migration: introduce postcopy-blocktime capability

[Eric Blake <eblake@redhat.com>]

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On 10/30/2017 08:16 AM, Alexey Perevalov wrote:
> Right now it could be used on destination side to
> enable vCPU blocktime calculation for postcopy live migration.
> vCPU blocktime - it's time since vCPU thread was put into
> interruptible sleep, till memory page was copied and thread awake.
> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Alexey Perevalov <a.perevalov@samsung.com>
> ---
>  migration/migration.c | 9 +++++++++
>  migration/migration.h | 1 +
>  qapi/migration.json   | 6 +++++-
>  3 files changed, 15 insertions(+), 1 deletion(-)
> 

Is there any reason this has to be a new capability rather than
unconditionally enabled?  What are the trade-offs for enabling vs.
disabling the capability that warrant it being a knob?  Can we do a
better job of documenting in which cases the user would want to change
the knob from its default value, if we even need it to be a knob?

> +++ b/qapi/migration.json
> @@ -352,12 +352,16 @@
>  #
>  # @x-multifd: Use more than one fd for migration (since 2.11)
>  #
> +# @postcopy-blocktime: Calculate downtime for postcopy live migration
> +#                     (since 2.11)
> +#
>  # Since: 1.2
>  ##
>  { 'enum': 'MigrationCapability',
>    'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
>             'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram',
> -           'block', 'return-path', 'pause-before-switchover', 'x-multifd' ] }
> +           'block', 'return-path', 'pause-before-switchover', 'x-multifd',
> +           'postcopy-blocktime' ] }
>  
>  ##
>  # @MigrationCapabilityStatus:
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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