migration/postcopy: Add max-postcopy-bandwidth parameter

Limit the background transfer bandwidth during the postcopy
phase to the value set on this new parameter.  The default, 0,
corresponds to the existing behaviour which is unlimited bandwidth.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20180613102642.23995-2-dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

hmp.c

@@ -370,6 +370,9 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, "%s: %" PRIu64 "\n",
             MigrationParameter_str(MIGRATION_PARAMETER_XBZRLE_CACHE_SIZE),
             params->xbzrle_cache_size);
+        monitor_printf(mon, "%s: %" PRIu64 "\n",
+            MigrationParameter_str(MIGRATION_PARAMETER_MAX_POSTCOPY_BANDWIDTH),
+            params->max_postcopy_bandwidth);
     }
 
     qapi_free_MigrationParameters(params);
@@ -1676,6 +1679,10 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
         }
         p->xbzrle_cache_size = cache_size;
         break;
+    case MIGRATION_PARAMETER_MAX_POSTCOPY_BANDWIDTH:
+        p->has_max_postcopy_bandwidth = true;
+        visit_type_size(v, param, &p->max_postcopy_bandwidth, &err);
+        break;
     default:
         assert(0);
     }

migration/migration.c

@@ -82,6 +82,11 @@
 #define DEFAULT_MIGRATE_MULTIFD_CHANNELS 2
 #define DEFAULT_MIGRATE_MULTIFD_PAGE_COUNT 16
 
+/* Background transfer rate for postcopy, 0 means unlimited, note
+ * that page requests can still exceed this limit.
+ */
+#define DEFAULT_MIGRATE_MAX_POSTCOPY_BANDWIDTH 0
+
 static NotifierList migration_state_notifiers =
     NOTIFIER_LIST_INITIALIZER(migration_state_notifiers);
 
@@ -659,6 +664,8 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->x_multifd_page_count = s->parameters.x_multifd_page_count;
     params->has_xbzrle_cache_size = true;
     params->xbzrle_cache_size = s->parameters.xbzrle_cache_size;
+    params->has_max_postcopy_bandwidth = true;
+    params->max_postcopy_bandwidth = s->parameters.max_postcopy_bandwidth;
 
     return params;
 }
@@ -1066,6 +1073,9 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
     if (params->has_xbzrle_cache_size) {
         dest->xbzrle_cache_size = params->xbzrle_cache_size;
     }
+    if (params->has_max_postcopy_bandwidth) {
+        dest->max_postcopy_bandwidth = params->max_postcopy_bandwidth;
+    }
 }
 
 static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
@@ -1138,6 +1148,9 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
         s->parameters.xbzrle_cache_size = params->xbzrle_cache_size;
         xbzrle_cache_resize(params->xbzrle_cache_size, errp);
     }
+    if (params->has_max_postcopy_bandwidth) {
+        s->parameters.max_postcopy_bandwidth = params->max_postcopy_bandwidth;
+    }
 }
 
 void qmp_migrate_set_parameters(MigrateSetParameters *params, Error **errp)
@@ -1887,6 +1900,16 @@ int64_t migrate_xbzrle_cache_size(void)
     return s->parameters.xbzrle_cache_size;
 }
 
+static int64_t migrate_max_postcopy_bandwidth(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.max_postcopy_bandwidth;
+}
+
+
 bool migrate_use_block(void)
 {
     MigrationState *s;
@@ -2226,6 +2249,7 @@ static int postcopy_start(MigrationState *ms)
     QIOChannelBuffer *bioc;
     QEMUFile *fb;
     int64_t time_at_stop = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+    int64_t bandwidth = migrate_max_postcopy_bandwidth();
     bool restart_block = false;
     int cur_state = MIGRATION_STATUS_ACTIVE;
     if (!migrate_pause_before_switchover()) {
@@ -2280,7 +2304,12 @@ static int postcopy_start(MigrationState *ms)
      * will notice we're in POSTCOPY_ACTIVE and not actually
      * wrap their state up here
      */
-    qemu_file_set_rate_limit(ms->to_dst_file, INT64_MAX);
+    /* 0 max-postcopy-bandwidth means unlimited */
+    if (!bandwidth) {
+        qemu_file_set_rate_limit(ms->to_dst_file, INT64_MAX);
+    } else {
+        qemu_file_set_rate_limit(ms->to_dst_file, bandwidth / XFER_LIMIT_RATIO);
+    }
     if (migrate_postcopy_ram()) {
         /* Ping just for debugging, helps line traces up */
         qemu_savevm_send_ping(ms->to_dst_file, 2);
@@ -3042,6 +3071,9 @@ static Property migration_properties[] = {
     DEFINE_PROP_SIZE("xbzrle-cache-size", MigrationState,
                       parameters.xbzrle_cache_size,
                       DEFAULT_MIGRATE_XBZRLE_CACHE_SIZE),
+    DEFINE_PROP_SIZE("max-postcopy-bandwidth", MigrationState,
+                      parameters.max_postcopy_bandwidth,
+                      DEFAULT_MIGRATE_MAX_POSTCOPY_BANDWIDTH),
 
     /* Migration capabilities */
     DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE),
@@ -3110,6 +3142,7 @@ static void migration_instance_init(Object *obj)
     params->has_x_multifd_channels = true;
     params->has_x_multifd_page_count = true;
     params->has_xbzrle_cache_size = true;
+    params->has_max_postcopy_bandwidth = true;
 
     qemu_sem_init(&ms->postcopy_pause_sem, 0);
     qemu_sem_init(&ms->postcopy_pause_rp_sem, 0);

qapi/migration.json

@@ -517,6 +517,9 @@
 #                     and a power of 2
 #                     (Since 2.11)
 #
+# @max-postcopy-bandwidth: Background transfer bandwidth during postcopy.
+#                     Defaults to 0 (unlimited).  In bytes per second.
+#                     (Since 3.0)
 # Since: 2.4
 ##
 { 'enum': 'MigrationParameter',
@@ -525,7 +528,7 @@
            'tls-creds', 'tls-hostname', 'max-bandwidth',
            'downtime-limit', 'x-checkpoint-delay', 'block-incremental',
            'x-multifd-channels', 'x-multifd-page-count',
-           'xbzrle-cache-size' ] }
+           'xbzrle-cache-size', 'max-postcopy-bandwidth' ] }
 
 ##
 # @MigrateSetParameters:
@@ -593,6 +596,10 @@
 #                     needs to be a multiple of the target page size
 #                     and a power of 2
 #                     (Since 2.11)
+#
+# @max-postcopy-bandwidth: Background transfer bandwidth during postcopy.
+#                     Defaults to 0 (unlimited).  In bytes per second.
+#                     (Since 3.0)
 # Since: 2.4
 ##
 # TODO either fuse back into MigrationParameters, or make
@@ -611,7 +618,8 @@
             '*block-incremental': 'bool',
             '*x-multifd-channels': 'int',
             '*x-multifd-page-count': 'int',
-            '*xbzrle-cache-size': 'size' } }
+            '*xbzrle-cache-size': 'size',
+            '*max-postcopy-bandwidth': 'size' } }
 
 ##
 # @migrate-set-parameters:
@@ -694,6 +702,10 @@
 #                     needs to be a multiple of the target page size
 #                     and a power of 2
 #                     (Since 2.11)
+#
+# @max-postcopy-bandwidth: Background transfer bandwidth during postcopy.
+#                     Defaults to 0 (unlimited).  In bytes per second.
+#                     (Since 3.0)
 # Since: 2.4
 ##
 { 'struct': 'MigrationParameters',
@@ -710,7 +722,8 @@
             '*block-incremental': 'bool' ,
             '*x-multifd-channels': 'uint8',
             '*x-multifd-page-count': 'uint32',
-            '*xbzrle-cache-size': 'size' } }
+            '*xbzrle-cache-size': 'size',
+            '*max-postcopy-bandwidth': 'size'  } }
 
 ##
 # @query-migrate-parameters: