[PATCH] migration: Fix qmp_query_migrate mbps value

[Fabiano Rosas]

The QMP command query_migrate might see incorrect throughput numbers
if it runs after we've set the migration completion status but before
migration_calculate_complete() has updated s->total_time and s->mbps.

The migration status would show COMPLETED, but the throughput value
would be the one from the last iteration and not the one from the
whole migration. This will usually be a larger value due to the time
period being smaller (one iteration).

Move migration_calculate_complete() earlier so that the status
MIGRATION_STATUS_COMPLETED is only emitted after the final counters
update.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
CI run: https://gitlab.com/farosas/qemu/-/pipelines/1182405776
---
 migration/migration.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index ab21de2cad..7486d59da0 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -102,6 +102,7 @@ static int migration_maybe_pause(MigrationState *s,
                                  int new_state);
 static void migrate_fd_cancel(MigrationState *s);
 static bool close_return_path_on_source(MigrationState *s);
+static void migration_calculate_complete(MigrationState *s);
 
 static void migration_downtime_start(MigrationState *s)
 {
@@ -2746,6 +2747,7 @@ static void migration_completion(MigrationState *s)
         migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
                           MIGRATION_STATUS_COLO);
     } else {
+        migration_calculate_complete(s);
         migrate_set_state(&s->state, current_active_state,
                           MIGRATION_STATUS_COMPLETED);
     }
@@ -2784,6 +2786,7 @@ static void bg_migration_completion(MigrationState *s)
         goto fail;
     }
 
+    migration_calculate_complete(s);
     migrate_set_state(&s->state, current_active_state,
                       MIGRATION_STATUS_COMPLETED);
     return;
@@ -2993,12 +2996,15 @@ static void migration_calculate_complete(MigrationState 
*s)
     int64_t end_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
     int64_t transfer_time;
 
+    /* QMP could read from these concurrently */
+    bql_lock();
     migration_downtime_end(s);
     s->total_time = end_time - s->start_time;
     transfer_time = s->total_time - s->setup_time;
     if (transfer_time) {
         s->mbps = ((double) bytes * 8.0) / transfer_time / 1000;
     }
+    bql_unlock();
 }
 
 static void update_iteration_initial_status(MigrationState *s)
@@ -3145,7 +3151,6 @@ static void migration_iteration_finish(MigrationState *s)
     bql_lock();
     switch (s->state) {
     case MIGRATION_STATUS_COMPLETED:
-        migration_calculate_complete(s);
         runstate_set(RUN_STATE_POSTMIGRATE);
         break;
     case MIGRATION_STATUS_COLO:
@@ -3189,9 +3194,6 @@ static void bg_migration_iteration_finish(MigrationState 
*s)
     bql_lock();
     switch (s->state) {
     case MIGRATION_STATUS_COMPLETED:
-        migration_calculate_complete(s);
-        break;
-
     case MIGRATION_STATUS_ACTIVE:
     case MIGRATION_STATUS_FAILED:
     case MIGRATION_STATUS_CANCELLED:
-- 
2.35.3