migration: Add save_live_complete_precopy_thread handler

This SaveVMHandler helps device provide its own asynchronous transmission
of the remaining data at the end of a precopy phase via multifd channels,
in parallel with the transfer done by save_live_complete_precopy handlers.

These threads are launched only when multifd device state transfer is
supported.

Management of these threads in done in the multifd migration code,
wrapping them in the generic thread pool.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/qemu-devel/eac74a4ca7edd8968bbf72aa07b9041c76364a16.1741124640.git.maciej.szmigiero@oracle.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

1 files changed, 39 insertions, 1 deletions

diff --git a/migration/savevm.c b/migration/savevm.c
index 1abc365570..5c4fdfd95e 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -37,6 +37,7 @@
 #include "migration/register.h"
 #include "migration/global_state.h"
 #include "migration/channel-block.h"
+#include "multifd.h"
 #include "ram.h"
 #include "qemu-file.h"
 #include "savevm.h"
@@ -1527,6 +1528,24 @@ int qemu_savevm_state_complete_precopy_iterable(QEMUFile *f, bool in_postcopy)
     int64_t start_ts_each, end_ts_each;
     SaveStateEntry *se;
     int ret;
+    bool multifd_device_state = multifd_device_state_supported();
+
+    if (multifd_device_state) {
+        QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
+            SaveLiveCompletePrecopyThreadHandler hdlr;
+
+            if (!se->ops || (in_postcopy && se->ops->has_postcopy &&
+                             se->ops->has_postcopy(se->opaque)) ||
+                !se->ops->save_live_complete_precopy_thread) {
+                continue;
+            }
+
+            hdlr = se->ops->save_live_complete_precopy_thread;
+            multifd_spawn_device_state_save_thread(hdlr,
+                                                   se->idstr, se->instance_id,
+                                                   se->opaque);
+        }
+    }
 
     QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
         if (!se->ops ||
@@ -1552,16 +1571,35 @@ int qemu_savevm_state_complete_precopy_iterable(QEMUFile *f, bool in_postcopy)
         save_section_footer(f, se);
         if (ret < 0) {
             qemu_file_set_error(f, ret);
-            return -1;
+            goto ret_fail_abort_threads;
         }
         end_ts_each = qemu_clock_get_us(QEMU_CLOCK_REALTIME);
         trace_vmstate_downtime_save("iterable", se->idstr, se->instance_id,
                                     end_ts_each - start_ts_each);
     }
 
+    if (multifd_device_state) {
+        if (migrate_has_error(migrate_get_current())) {
+            multifd_abort_device_state_save_threads();
+        }
+
+        if (!multifd_join_device_state_save_threads()) {
+            qemu_file_set_error(f, -EINVAL);
+            return -1;
+        }
+    }
+
     trace_vmstate_downtime_checkpoint("src-iterable-saved");
 
     return 0;
+
+ret_fail_abort_threads:
+    if (multifd_device_state) {
+        multifd_abort_device_state_save_threads();
+        multifd_join_device_state_save_threads();
+    }
+
+    return -1;
 }
 
 int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,