commit 94f5a43704129ca4995aa3385303c5ae225bde42
author Liang Li <liang.z.li@intel.com> Mon Nov 02 15:37:00 2015 +0800
committer Juan Quintela <quintela@redhat.com> Wed Nov 04 13:40:13 2015 +0100
tree 84258ec091fadb00976a785a320c66211f58174d
parent 79cf9fad341e6e7bd6b55395b71d5c5727d7f5b0

migration: defer migration_end & blk_mig_cleanup

Because of the patch 3ea3b7fa9af067982f34b of kvm, which introduces a
lazy collapsing of small sptes into large sptes mechanism, now
migration_end() is a time consuming operation because it calls
memroy_global_dirty_log_stop(), which will trigger the dropping of small
sptes operation and takes about dozens of milliseconds, so call
migration_end() before all the vmsate data has already been transferred
to the destination will prolong VM downtime. This operation should be
deferred after all the data has been transferred to the destination.

blk_mig_cleanup() can be deferred too.

For a VM with 8G RAM, this patch can reduce the VM downtime about 30 ms.

Signed-off-by: Liang Li <liang.z.li@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>al3
Reviewed-by: Amit Shah <amit.shah@redhat.com>al3
Signed-off-by: Juan Quintela <quintela@redhat.com>al3

migration/block.c

diff --git a/migration/block.c b/migration/block.c
index f7bb1e0..8401597 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -750,7 +750,6 @@
 
     qemu_put_be64(f, BLK_MIG_FLAG_EOS);
 
-    blk_mig_cleanup();
     return 0;
 }
 

migration/migration.c

diff --git a/migration/migration.c b/migration/migration.c
index b092f38..d5a7304 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -613,12 +613,9 @@
 
     assert(s->state != MIGRATION_STATUS_ACTIVE);
 
-    if (s->state != MIGRATION_STATUS_COMPLETED) {
-        qemu_savevm_state_cancel();
-        if (s->state == MIGRATION_STATUS_CANCELLING) {
-            migrate_set_state(s, MIGRATION_STATUS_CANCELLING,
-                              MIGRATION_STATUS_CANCELLED);
-        }
+    if (s->state == MIGRATION_STATUS_CANCELLING) {
+        migrate_set_state(s, MIGRATION_STATUS_CANCELLING,
+                          MIGRATION_STATUS_CANCELLED);
     }
 
     notifier_list_notify(&migration_state_notifiers, s);
@@ -1028,6 +1025,7 @@
     int64_t initial_bytes = 0;
     int64_t max_size = 0;
     int64_t start_time = initial_time;
+    int64_t end_time;
     bool old_vm_running = false;
 
     rcu_register_thread();
@@ -1089,10 +1087,11 @@
 
     /* If we enabled cpu throttling for auto-converge, turn it off. */
     cpu_throttle_stop();
+    end_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
 
     qemu_mutex_lock_iothread();
+    qemu_savevm_state_cancel();
     if (s->state == MIGRATION_STATUS_COMPLETED) {
-        int64_t end_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
         uint64_t transferred_bytes = qemu_ftell(s->file);
         s->total_time = end_time - s->total_time;
         s->downtime = end_time - start_time;

migration/ram.c

diff --git a/migration/ram.c b/migration/ram.c
index a25bcc7..25e9eeb 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1344,7 +1344,6 @@
 
     rcu_read_unlock();
 
-    migration_end();
     qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
 
     return 0;