Re: [PATCH 1/2] migration/colo: Optimize COLO start code path

[Juan Quintela <quintela@redhat.com>]

Zhang Chen <chen.zhang@intel.com> wrote:
> There is no need to start COLO through MIGRATION_STATUS_ACTIVE.

Hi

I don't understand what you are trying to do.  In my reading, at least
the commit message is wrong:

void migrate_start_colo_process(MigrationState *s)
{
    ...
    migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
                      MIGRATION_STATUS_COLO);
    ...
}

and

void *colo_process_incoming_thread(void *opaque)
{
    ...
    migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
                      MIGRATION_STATUS_COLO);

So colo starts with MIGRATION_STATUS_ACTIVE.


> Signed-off-by: Zhang Chen <chen.zhang@intel.com>
> ---
>  migration/colo.c      |  2 --
>  migration/migration.c | 18 +++++++++++-------
>  2 files changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/migration/colo.c b/migration/colo.c
> index 2415325262..ad1a4426b3 100644
> --- a/migration/colo.c
> +++ b/migration/colo.c
> @@ -667,8 +667,6 @@ void migrate_start_colo_process(MigrationState *s)
>                                  colo_checkpoint_notify, s);
>  
>      qemu_sem_init(&s->colo_exit_sem, 0);
> -    migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
> -                      MIGRATION_STATUS_COLO);
>      colo_process_checkpoint(s);
>      qemu_mutex_lock_iothread();
>  }
> diff --git a/migration/migration.c b/migration/migration.c
> index abaf6f9e3d..4c8662a839 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -3222,7 +3222,10 @@ static void migration_completion(MigrationState *s)
>          goto fail_invalidate;
>      }
>  
> -    if (!migrate_colo_enabled()) {
> +    if (migrate_colo_enabled()) {
> +        migrate_set_state(&s->state, current_active_state,
> +                          MIGRATION_STATUS_COLO);
> +    } else {
>          migrate_set_state(&s->state, current_active_state,
>                            MIGRATION_STATUS_COMPLETED);
>      }

This moves the setup to MIGRATION_STATUS_COLO to completion time instead
of the beggining of the process.  I have no clue why.  I guess you can
put a comment/commit message to say what you ar.e trynig to do.

> @@ -3607,12 +3610,7 @@ static void migration_iteration_finish(MigrationState *s)
>          migration_calculate_complete(s);
>          runstate_set(RUN_STATE_POSTMIGRATE);
>          break;
> -
> -    case MIGRATION_STATUS_ACTIVE:
> -        /*
> -         * We should really assert here, but since it's during
> -         * migration, let's try to reduce the usage of assertions.
> -         */
> +    case MIGRATION_STATUS_COLO:
>          if (!migrate_colo_enabled()) {
>              error_report("%s: critical error: calling COLO code without "
>                           "COLO enabled", __func__);
> @@ -3622,6 +3620,12 @@ static void migration_iteration_finish(MigrationState *s)
>           * Fixme: we will run VM in COLO no matter its old running state.
>           * After exited COLO, we will keep running.
>           */
> +         /* Fallthrough */
> +    case MIGRATION_STATUS_ACTIVE:
> +        /*
> +         * We should really assert here, but since it's during
> +         * migration, let's try to reduce the usage of assertions.
> +         */
>          s->vm_was_running = true;
>          /* Fallthrough */
>      case MIGRATION_STATUS_FAILED:

I guess this change is related to the previous one, but I don't
understand colo enough to review it.

Later, Juan.