Re: [PATCH v2 2/3] Add zero-copy-copied migration stat

[Markus Armbruster]

Leonardo Bras <leobras@redhat.com> writes:

> Signed-off-by: Leonardo Bras <leobras@redhat.com>
> ---
>  qapi/migration.json   | 5 ++++-
>  migration/migration.c | 1 +
>  monitor/hmp-cmds.c    | 4 ++++
>  3 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 7102e474a6..925f009868 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -55,6 +55,9 @@
>  # @postcopy-bytes: The number of bytes sent during the post-copy phase
>  #                  (since 7.0).
>  #
> +# @zero-copy-copied: The number of zero-copy flushes that reported data sent
> +#                    using zero-copy that ended up being copied. (since 7.2)

The description feels awkward.  What's a "zero-copy flush", and why
should the user care?  I figure what users care about is the number of
all-zero pages we had to "copy", i.e. send the bulky way.  Is this what
@zero-copy-copied reports?

> +#
>  # Since: 0.14
>  ##
>  { 'struct': 'MigrationStats',
> @@ -65,7 +68,7 @@
>             'postcopy-requests' : 'int', 'page-size' : 'int',
>             'multifd-bytes' : 'uint64', 'pages-per-second' : 'uint64',
>             'precopy-bytes' : 'uint64', 'downtime-bytes' : 'uint64',
> -           'postcopy-bytes' : 'uint64' } }
> +           'postcopy-bytes' : 'uint64', 'zero-copy-copied' : 'uint64' } }
>  
>  ##
>  # @XBZRLECacheStats: