Re: [Qemu-devel] [RFC 10/29] migration: new property "x-postcopy-fast"

[Dr. David Alan Gilbert]

* Peter Xu (address@hidden) wrote:
> This provides a way to start postcopy ASAP when migration starts. To do
> this, we need both:
> 
>   -global migration.x-postcopy-ram=on \
>   -global migration.x-postcopy-fast=on

Can you explain why this is necessary?  Both sides already know
they're doing a postcopy recovery don't they?

Dave

> 
> Signed-off-by: Peter Xu <address@hidden>
> ---
>  migration/migration.c | 9 ++++++++-
>  migration/migration.h | 2 ++
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 5b2602e..efee87e 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1936,6 +1936,11 @@ bool migrate_colo_enabled(void)
>      return s->enabled_capabilities[MIGRATION_CAPABILITY_X_COLO];
>  }
>  
> +static bool postcopy_should_start(MigrationState *s)
> +{
> +    return atomic_read(&s->start_postcopy) || s->start_postcopy_fast;
> +}
> +
>  /*
>   * Master migration thread on the source VM.
>   * It drives the migration and pumps the data down the outgoing channel.
> @@ -2013,7 +2018,7 @@ static void *migration_thread(void *opaque)
>                  if (migrate_postcopy_ram() &&
>                      s->state != MIGRATION_STATUS_POSTCOPY_ACTIVE &&
>                      pend_nonpost <= threshold_size &&
> -                    atomic_read(&s->start_postcopy)) {
> +                    postcopy_should_start(s)) {
>  
>                      if (!postcopy_start(s, &old_vm_running)) {
>                          current_active_state = 
> MIGRATION_STATUS_POSTCOPY_ACTIVE;
> @@ -2170,6 +2175,8 @@ static Property migration_properties[] = {
>                       send_configuration, true),
>      DEFINE_PROP_BOOL("send-section-footer", MigrationState,
>                       send_section_footer, true),
> +    DEFINE_PROP_BOOL("x-postcopy-fast", MigrationState,
> +                     start_postcopy_fast, false),
>  
>      /* Migration parameters */
>      DEFINE_PROP_INT64("x-compress-level", MigrationState,
> diff --git a/migration/migration.h b/migration/migration.h
> index 70e3094..e902bae 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -113,6 +113,8 @@ struct MigrationState
>  
>      /* Flag set once the migration has been asked to enter postcopy */
>      bool start_postcopy;
> +    /* Set the flag if we want to start postcopy ASAP when migration starts 
> */
> +    bool start_postcopy_fast;
>      /* Flag set after postcopy has sent the device state */
>      bool postcopy_after_devices;
>  
> -- 
> 2.7.4
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK