Re: [Qemu-devel] [PATCH V5 5/9] migration: introduce postcopy-blocktime capability

[Eric Blake]

On 05/12/2017 08:31 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.
> 
> Signed-off-by: Alexey Perevalov <address@hidden>
> ---
>  include/migration/migration.h | 1 +
>  migration/migration.c         | 9 +++++++++
>  qapi-schema.json              | 5 ++++-
>  3 files changed, 14 insertions(+), 1 deletion(-)
> 

> +++ b/qapi-schema.json
> @@ -894,11 +894,14 @@
>  # @release-ram: if enabled, qemu will free the migrated ram pages on the 
> source
>  #        during postcopy-ram migration. (since 2.9)
>  #
> +# @postcopy-blocktime: Calculate downtime for postcopy live migration (since 
> 2.10)
> +#
>  # Since: 1.2
>  ##
>  { 'enum': 'MigrationCapability',
>    'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
> -           'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram'] }
> +           'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram',
> +           'postcopy-blocktime'] }

Why does this need to be a capability that we have to turn on, and not
something that is collected unconditionally? Is there a drawback to
having the stat collection always enabled without a capability?

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

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