[Qemu-devel] [PATCH 5/6] migration: send postcopy downtime back to source

[Alexey Perevalov]

Right now to initiate postcopy live migration need to
send request to source machine and specify destination.

User could request migration status by query-migrate qmp command on
source machine, but postcopy downtime is being evaluated on destination,
so it should be transmitted back to source. For this purpose return path
socket was shosen.

Signed-off-by: Alexey Perevalov <address@hidden>
---
 include/migration/migration.h |  4 +++-
 migration/migration.c         | 20 ++++++++++++++++++--
 migration/postcopy-ram.c      |  1 +
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 5d2c628..5535aa6 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -55,7 +55,8 @@ enum mig_rp_message_type {
 
     MIG_RP_MSG_REQ_PAGES_ID, /* data (start: be64, len: be32, id: string) */
     MIG_RP_MSG_REQ_PAGES,    /* data (start: be64, len: be32) */
-
+    MIG_RP_MSG_DOWNTIME,    /* downtime value from destination,
+                               calculated and sent in case of post copy */
     MIG_RP_MSG_MAX
 };
 
@@ -364,6 +365,7 @@ void migrate_send_rp_pong(MigrationIncomingState *mis,
                           uint32_t value);
 void migrate_send_rp_req_pages(MigrationIncomingState *mis, const char* rbname,
                               ram_addr_t start, size_t len);
+void migrate_send_rp_downtime(MigrationIncomingState *mis, uint64_t downtime);
 
 void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
 void ram_control_after_iterate(QEMUFile *f, uint64_t flags);
diff --git a/migration/migration.c b/migration/migration.c
index 5bac434..3134e24 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -553,6 +553,19 @@ void migrate_send_rp_message(MigrationIncomingState *mis,
 }
 
 /*
+ * Send postcopy migration downtime,
+ * at the moment of calling this function migration should
+ * be completed.
+ */
+void migrate_send_rp_downtime(MigrationIncomingState *mis, uint64_t downtime)
+{
+    uint64_t buf;
+
+    buf = cpu_to_be64(downtime);
+    migrate_send_rp_message(mis, MIG_RP_MSG_DOWNTIME, sizeof(downtime), &buf);
+}
+
+/*
  * Send a 'SHUT' message on the return channel with the given value
  * to indicate that we've finished with the RP.  Non-0 value indicates
  * error.
@@ -1483,6 +1496,7 @@ static struct rp_cmd_args {
     [MIG_RP_MSG_PONG]           = { .len =  4, .name = "PONG" },
     [MIG_RP_MSG_REQ_PAGES]      = { .len = 12, .name = "REQ_PAGES" },
     [MIG_RP_MSG_REQ_PAGES_ID]   = { .len = -1, .name = "REQ_PAGES_ID" },
+    [MIG_RP_MSG_DOWNTIME]       = { .len =  8, .name = "DOWNTIME" },
     [MIG_RP_MSG_MAX]            = { .len = -1, .name = "MAX" },
 };
 
@@ -1613,6 +1627,10 @@ static void *source_return_path_thread(void *opaque)
             migrate_handle_rp_req_pages(ms, (char *)&buf[13], start, len);
             break;
 
+        case MIG_RP_MSG_DOWNTIME:
+            ms->downtime = ldq_be_p(buf);
+            break;
+
         default:
             break;
         }
@@ -1677,7 +1695,6 @@ static int postcopy_start(MigrationState *ms, bool 
*old_vm_running)
     int ret;
     QIOChannelBuffer *bioc;
     QEMUFile *fb;
-    int64_t time_at_stop = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
     bool restart_block = false;
     migrate_set_state(&ms->state, MIGRATION_STATUS_ACTIVE,
                       MIGRATION_STATUS_POSTCOPY_ACTIVE);
@@ -1779,7 +1796,6 @@ static int postcopy_start(MigrationState *ms, bool 
*old_vm_running)
      */
     ms->postcopy_after_devices = true;
     notifier_list_notify(&migration_state_notifiers, ms);
-    ms->downtime =  qemu_clock_get_ms(QEMU_CLOCK_REALTIME) - time_at_stop;
 
     qemu_mutex_unlock_iothread();
 
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index ea89f4e..42330fd 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -330,6 +330,7 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState 
*mis)
     }
 
     postcopy_state_set(POSTCOPY_INCOMING_END);
+    migrate_send_rp_downtime(mis, get_postcopy_total_downtime());
     migrate_send_rp_shut(mis, qemu_file_get_error(mis->from_src_file) != 0);
 
     if (mis->postcopy_tmp_page) {
-- 
1.8.3.1