[PATCH v4 3/4] multifd: Only sync once each full round of memory

[Juan Quintela]

We need to add a new flag to mean to sync at that point.
Notice that we still synchronize at the end of setup and at the end of
complete stages.

Signed-off-by: Juan Quintela <quintela@redhat.com>

---

Add missing qemu_fflush(), now it passes all tests always.
---
 qapi/migration.json   |  2 +-
 migration/migration.c |  2 --
 migration/ram.c       | 28 +++++++++++++++++++++++++++-
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/qapi/migration.json b/qapi/migration.json
index 2907241b9c..5d0efa4590 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -482,7 +482,7 @@
 #                                   section is sent.  We used to do
 #                                   that in the past, but it is
 #                                   suboptimal.
-#                                   Default value is true until all code is in.
+#                                   Default value is false.
 #                                   (since 8.0)
 #
 # Features:
diff --git a/migration/migration.c b/migration/migration.c
index b2844d374f..9eb061319d 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2710,8 +2710,6 @@ bool migrate_multifd_sync_after_each_section(void)
 {
     MigrationState *s = migrate_get_current();
 
-    return true;
-    // We will change this when code gets in.
     return 
s->enabled_capabilities[MIGRATION_CAPABILITY_MULTIFD_SYNC_AFTER_EACH_SECTION];
 }
 
diff --git a/migration/ram.c b/migration/ram.c
index 899e2cd8af..32fab7b5ee 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -82,6 +82,7 @@
 #define RAM_SAVE_FLAG_XBZRLE   0x40
 /* 0x80 is reserved in migration.h start with 0x100 next */
 #define RAM_SAVE_FLAG_COMPRESS_PAGE    0x100
+#define RAM_SAVE_FLAG_MULTIFD_SYNC     0x200
 
 int (*xbzrle_encode_buffer_func)(uint8_t *, uint8_t *, int,
      uint8_t *, int) = xbzrle_encode_buffer;
@@ -1593,6 +1594,7 @@ retry:
  * associated with the search process.
  *
  * Returns:
+ *         <0: An error happened
  *         PAGE_ALL_CLEAN: no dirty page found, give up
  *         PAGE_TRY_AGAIN: no dirty page found, retry for next block
  *         PAGE_DIRTY_FOUND: dirty page found
@@ -1620,6 +1622,15 @@ static int find_dirty_block(RAMState *rs, 
PageSearchStatus *pss)
         pss->page = 0;
         pss->block = QLIST_NEXT_RCU(pss->block, next);
         if (!pss->block) {
+            if (!migrate_multifd_sync_after_each_section()) {
+                QEMUFile *f = rs->pss[RAM_CHANNEL_PRECOPY].pss_channel;
+                int ret = multifd_send_sync_main(f);
+                if (ret < 0) {
+                    return ret;
+                }
+                qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_SYNC);
+                qemu_fflush(f);
+            }
             /*
              * If memory migration starts over, we will meet a dirtied page
              * which may still exists in compression threads's ring, so we
@@ -2612,6 +2623,9 @@ static int ram_find_and_save_block(RAMState *rs)
                     break;
                 } else if (res == PAGE_TRY_AGAIN) {
                     continue;
+                } else if (res < 0) {
+                    pages = res;
+                    break;
                 }
             }
         }
@@ -3298,6 +3312,10 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
         return ret;
     }
 
+    if (!migrate_multifd_sync_after_each_section()) {
+        qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_SYNC);
+    }
+
     qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
     qemu_fflush(f);
 
@@ -3483,6 +3501,9 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
         return ret;
     }
 
+    if (!migrate_multifd_sync_after_each_section()) {
+        qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_SYNC);
+    }
     qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
     qemu_fflush(f);
 
@@ -4167,7 +4188,9 @@ int ram_load_postcopy(QEMUFile *f, int channel)
             }
             decompress_data_with_multi_threads(f, page_buffer, len);
             break;
-
+        case RAM_SAVE_FLAG_MULTIFD_SYNC:
+            multifd_recv_sync_main();
+            break;
         case RAM_SAVE_FLAG_EOS:
             /* normal exit */
             if (migrate_multifd_sync_after_each_section()) {
@@ -4441,6 +4464,9 @@ static int ram_load_precopy(QEMUFile *f)
                 break;
             }
             break;
+        case RAM_SAVE_FLAG_MULTIFD_SYNC:
+            multifd_recv_sync_main();
+            break;
         case RAM_SAVE_FLAG_EOS:
             /* normal exit */
             if (migrate_multifd_sync_after_each_section()) {
-- 
2.39.1