Re: [PATCH v7 3/5] migration: Add zero-copy parameter for QMP/HMP for Linux

From: Peter Xu <peterx@redhat.com>
To: Leonardo Bras <leobras@redhat.com>
Cc: "Daniel P. Berrangé" <berrange@redhat.com>,
	"Juan Quintela" <quintela@redhat.com>,
	"Markus Armbruster" <armbru@redhat.com>,
	qemu-devel@nongnu.org,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	"Eric Blake" <eblake@redhat.com>
Subject: Re: [PATCH v7 3/5] migration: Add zero-copy parameter for QMP/HMP for Linux
Date: Thu, 13 Jan 2022 15:00:18 +0800	[thread overview]
Message-ID: <Yd/OAt8z35orDwOM@xz-m1.local> (raw)
In-Reply-To: <20220106221341.8779-4-leobras@redhat.com>

On Thu, Jan 06, 2022 at 07:13:40PM -0300, Leonardo Bras wrote:
> Add property that allows zero-copy migration of memory pages,
> and also includes a helper function migrate_use_zero_copy() to check
> if it's enabled.
> 
> No code is introduced to actually do the migration, but it allow
> future implementations to enable/disable this feature.
> 
> On non-Linux builds this parameter is compiled-out.

I feel sad every time seeing a new parameter needs to be mostly duplicated 3
times in the code. :(

> diff --git a/migration/socket.c b/migration/socket.c
> index 05705a32d8..f7a77aafd3 100644
> --- a/migration/socket.c
> +++ b/migration/socket.c
> @@ -77,6 +77,11 @@ static void socket_outgoing_migration(QIOTask *task,
>      } else {
>          trace_migration_socket_outgoing_connected(data->hostname);
>      }
> +
> +    if (migrate_use_zero_copy()) {
> +        error_setg(&err, "Zero copy not available in migration");
> +    }

I got confused the 1st time looking at it..  I think this is not strongly
needed, but that's okay:

Reviewed-by: Peter Xu <peterx@redhat.com>

Thanks,

-- 
Peter Xu