[PATCH v2 1/5] migration: Set downtime_start even for postcopy

[Peter Xu <peterx@redhat.com>]

Postcopy calculates its downtime separately.  It always sets
MigrationState.downtime properly, but not MigrationState.downtime_start.

Make postcopy do the same as other modes on properly recording the
timestamp when the VM is going to be stopped.  Drop the temporary variable
in postcopy_start() along the way.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/migration.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 67547eb6a1..f8a54ff4d1 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2121,7 +2121,6 @@ static int postcopy_start(MigrationState *ms, Error **errp)
     int ret;
     QIOChannelBuffer *bioc;
     QEMUFile *fb;
-    int64_t time_at_stop = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
     uint64_t bandwidth = migrate_max_postcopy_bandwidth();
     bool restart_block = false;
     int cur_state = MIGRATION_STATUS_ACTIVE;
@@ -2143,6 +2142,8 @@ static int postcopy_start(MigrationState *ms, Error **errp)
     qemu_mutex_lock_iothread();
     trace_postcopy_start_set_run();
 
+    ms->downtime_start = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+
     qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
     global_state_store();
     ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
@@ -2245,7 +2246,7 @@ static int postcopy_start(MigrationState *ms, Error **errp)
     ms->postcopy_after_devices = true;
     migration_call_notifiers(ms);
 
-    ms->downtime =  qemu_clock_get_ms(QEMU_CLOCK_REALTIME) - time_at_stop;
+    ms->downtime = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) - ms->downtime_start;
 
     qemu_mutex_unlock_iothread();
 
-- 
2.41.0