[Qemu-devel] [RFC/COLO: 3/3] COLO: Parameterise background RAM transfer limit

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

COLO (experimentally) transfers RAM in the background when the amount
to transfer reaches a limit; allow this limit to be set via the
parameter mechanism.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 hmp.c                 |  8 ++++++++
 migration/colo.c      |  6 ++----
 migration/migration.c | 19 +++++++++++++++++++
 qapi-schema.json      | 13 ++++++++++---
 4 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/hmp.c b/hmp.c
index 0e92d11..c177fbf 100644
--- a/hmp.c
+++ b/hmp.c
@@ -307,6 +307,9 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, " %s: %" PRId64,
             MigrationParameter_lookup[MIGRATION_PARAMETER_COLO_RELAX_TIME],
             params->colo_relax_time);
+        monitor_printf(mon, " %s: %" PRId64,
+            MigrationParameter_lookup[MIGRATION_PARAMETER_COLO_RAM_LIVE],
+            params->colo_ram_live);
 
         monitor_printf(mon, "\n");
     }
@@ -1263,6 +1266,7 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
     bool has_colo_min_time = false;
     bool has_colo_max_time = false;
     bool has_colo_relax_time = false;
+    bool has_colo_ram_live = false;
 
     int i;
 
@@ -1296,6 +1300,9 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
             case MIGRATION_PARAMETER_COLO_RELAX_TIME:
                 has_colo_relax_time = true;
                 break;
+            case MIGRATION_PARAMETER_COLO_RAM_LIVE:
+                has_colo_ram_live = true;
+                break;
             }
             qmp_migrate_set_parameters(has_compress_level, value,
                                        has_compress_threads, value,
@@ -1306,6 +1313,7 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
                                        has_colo_min_time, value,
                                        has_colo_max_time, value,
                                        has_colo_relax_time, value,
+                                       has_colo_ram_live, value,
                                        &err);
             break;
         }
diff --git a/migration/colo.c b/migration/colo.c
index 5c8096d..9db9de1 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -486,13 +486,11 @@ static bool checkpoint_choice(MigrationState *s)
     }
 }
 
-/* should be calculated by bandwidth and max downtime ? */
-#define THRESHOLD_PENDING_SIZE (10 * 1024 * 1024UL)
-
 static int colo_need_live_migrate_ram(MigrationState *s)
 {
     uint64_t pending_size;
-    int64_t max_size = THRESHOLD_PENDING_SIZE;
+    int64_t max_size = s->parameters[MIGRATION_PARAMETER_COLO_RAM_LIVE] *
+                       1024 * 1024;
 
     pending_size = qemu_savevm_state_pending(s->file, max_size);
     return (pending_size && pending_size >= max_size);
diff --git a/migration/migration.c b/migration/migration.c
index d41914c..d4214be 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -61,6 +61,8 @@
 #define DEFAULT_MIGRATE_COLO_MAX_TIME 10000
 /* Time after a miscompare before resuming comparison (ms) */
 #define DEFAULT_MIGRATE_COLO_RELAX_TIME 100
+/* Amount of RAM changes to trigger background RAM transfer (MiB) */ 
+#define DEFAULT_MIGRATE_COLO_RAM_LIVE 10
 
 static NotifierList migration_state_notifiers =
     NOTIFIER_LIST_INITIALIZER(migration_state_notifiers);
@@ -97,6 +99,8 @@ MigrationState *migrate_get_current(void)
                 DEFAULT_MIGRATE_COLO_MAX_TIME,
         .parameters[MIGRATION_PARAMETER_COLO_RELAX_TIME] =
                 DEFAULT_MIGRATE_COLO_RELAX_TIME,
+        .parameters[MIGRATION_PARAMETER_COLO_RAM_LIVE] =
+                DEFAULT_MIGRATE_COLO_RAM_LIVE,
         .checkpoint_state.max_downtime = 0,
         .checkpoint_state.min_downtime = INT64_MAX
     };
@@ -420,6 +424,7 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->colo_min_time = s->parameters[MIGRATION_PARAMETER_COLO_MIN_TIME];
     params->colo_max_time = s->parameters[MIGRATION_PARAMETER_COLO_MAX_TIME];
     params->colo_relax_time = s->parameters[MIGRATION_PARAMETER_COLO_RELAX_TIME];
+    params->colo_ram_live = s->parameters[MIGRATION_PARAMETER_COLO_RAM_LIVE];
 
     return params;
 }
@@ -583,6 +588,8 @@ void qmp_migrate_set_parameters(bool has_compress_level,
                                 int64_t colo_max_time,
                                 bool has_colo_relax_time,
                                 int64_t colo_relax_time,
+                                bool has_colo_ram_live,
+                                int64_t colo_ram_live,
                                 Error **errp)
 {
     MigrationState *s = migrate_get_current();
@@ -636,6 +643,11 @@ void qmp_migrate_set_parameters(bool has_compress_level,
                   "colo_relax_time",
                   "is invalid, it must be positive");
     }
+    if (has_colo_ram_live && (colo_ram_live < 0)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                  "colo_ram_live",
+                  "is invalid, it must be positive");
+    }
 
     if (has_compress_level) {
         s->parameters[MIGRATION_PARAMETER_COMPRESS_LEVEL] = compress_level;
@@ -671,6 +683,10 @@ void qmp_migrate_set_parameters(bool has_compress_level,
         s->parameters[MIGRATION_PARAMETER_COLO_RELAX_TIME] =
                                                     colo_relax_time;
     }
+    if (has_colo_ram_live) {
+        s->parameters[MIGRATION_PARAMETER_COLO_RAM_LIVE] =
+                                                    colo_ram_live;
+    }
 }
 
 /* shared migration helpers */
@@ -799,6 +815,8 @@ static MigrationState *migrate_init(const MigrationParams *params)
                             MIGRATION_PARAMETER_COLO_MAX_TIME];
     int64_t colo_relax_time = s->parameters[
                             MIGRATION_PARAMETER_COLO_RELAX_TIME];
+    int64_t colo_ram_live = s->parameters[
+                            MIGRATION_PARAMETER_COLO_RAM_LIVE];
 
     memcpy(enabled_capabilities, s->enabled_capabilities,
            sizeof(enabled_capabilities));
@@ -821,6 +839,7 @@ static MigrationState *migrate_init(const MigrationParams *params)
     s->parameters[MIGRATION_PARAMETER_COLO_MIN_TIME] = colo_min_time;
     s->parameters[MIGRATION_PARAMETER_COLO_MAX_TIME] = colo_max_time;
     s->parameters[MIGRATION_PARAMETER_COLO_RELAX_TIME] = colo_relax_time;
+    s->parameters[MIGRATION_PARAMETER_COLO_RAM_LIVE] = colo_ram_live;
 
     s->bandwidth_limit = bandwidth_limit;
     migrate_set_state(&s->state, MIGRATION_STATUS_NONE, MIGRATION_STATUS_SETUP);
diff --git a/qapi-schema.json b/qapi-schema.json
index 30113fc..bd264d0 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -636,13 +636,15 @@
 # @colo-min-time: Minimum Time (in ms) for a COLO comparative checkpoint
 # @colo-max-time: Maximum Time (in ms) for a COLO comparative checkpoint
 # @colo-relax-time: Time (in ms) after a miscompare before starting a new COLO checkpoint
+# @colo-ram-live: Amount of RAM changes to trigger background RAM transfer (MiB)
 #
 # Since: 2.4
 ##
 { 'enum': 'MigrationParameter',
   'data': ['compress-level', 'compress-threads', 'decompress-threads',
            'colo-passive-count', 'colo-passive-limit', 'colo-passive-time',
-           'colo-min-time', 'colo-max-time', 'colo-relax-time' ] }
+           'colo-min-time', 'colo-max-time', 'colo-relax-time',
+           'colo-ram-live' ] }
 
 #
 # @migrate-set-parameters
@@ -661,6 +663,7 @@
 # @colo-min-time: Minimum Time (in ms) for a COLO comparative checkpoint
 # @colo-max-time: Maximum Time (in ms) for a COLO comparative checkpoint
 # @colo-relax-time: Time (in ms) after a miscompare before starting a new COLO checkpoint
+# @colo-ram-live: Amount of RAM changes to trigger background RAM transfer (MiB)
 #
 # Since: 2.4
 ##
@@ -673,7 +676,8 @@
             '*colo-passive-time': 'int',
             '*colo-min-time': 'int',
             '*colo-max-time': 'int',
-            '*colo-relax-time': 'int'
+            '*colo-relax-time': 'int',
+            '*colo-ram-live': 'int'
           } }
 
 #
@@ -685,6 +689,8 @@
 #
 # @decompress-threads: decompression thread count
 #
+# @colo-ram-live: Amount of RAM changes to trigger background RAM transfer (MiB)
+#
 # Since: 2.4
 ##
 { 'struct': 'MigrationParameters',
@@ -696,7 +702,8 @@
             'colo-passive-time': 'int',
             'colo-min-time': 'int',
             'colo-max-time': 'int',
-            'colo-relax-time': 'int' } }
+            'colo-relax-time': 'int',
+            'colo-ram-live': 'int' } }
 
 ##
 # @query-migrate-parameters
-- 
2.4.3