[PATCH] migration: Do not perform RAMBlock dirty sync during the first iteration

[yong.huang@smartx.com]

From: Hyman Huang <yong.huang@smartx.com>

The first iteration's RAMBlock dirty sync can be omitted because QEMU
always initializes the RAMBlock's bmap to all 1s by default.

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
---
 migration/cpu-throttle.c |  2 +-
 migration/ram.c          | 19 ++++++++++++++++---
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/migration/cpu-throttle.c b/migration/cpu-throttle.c
index 5179019e33..674dc2004e 100644
--- a/migration/cpu-throttle.c
+++ b/migration/cpu-throttle.c
@@ -141,7 +141,7 @@ void cpu_throttle_dirty_sync_timer_tick(void *opaque)
      * effect on guest performance, therefore omit it to avoid
      * paying extra for the sync penalty.
      */
-    if (sync_cnt <= 1) {
+    if (!sync_cnt) {
         goto end;
     }
 
diff --git a/migration/ram.c b/migration/ram.c
index 05ff9eb328..a0123eb93e 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2718,7 +2718,7 @@ static void ram_list_init_bitmaps(void)
 {
     MigrationState *ms = migrate_get_current();
     RAMBlock *block;
-    unsigned long pages;
+    unsigned long pages, clear_bmap_pages;
     uint8_t shift;
 
     /* Skip setting bitmap if there is no RAM */
@@ -2736,6 +2736,7 @@ static void ram_list_init_bitmaps(void)
 
         RAMBLOCK_FOREACH_NOT_IGNORED(block) {
             pages = block->max_length >> TARGET_PAGE_BITS;
+            clear_bmap_pages = clear_bmap_size(pages, shift);
             /*
              * The initial dirty bitmap for migration must be set with all
              * ones to make sure we'll migrate every guest RAM page to
@@ -2751,7 +2752,12 @@ static void ram_list_init_bitmaps(void)
                 block->file_bmap = bitmap_new(pages);
             }
             block->clear_bmap_shift = shift;
-            block->clear_bmap = bitmap_new(clear_bmap_size(pages, shift));
+            block->clear_bmap = bitmap_new(clear_bmap_pages);
+            /*
+             * Set clear_bmap to 1 unconditionally, as we always set bmap
+             * to all 1s by default.
+             */
+            bitmap_set(block->clear_bmap, 0, clear_bmap_pages);
         }
     }
 }
@@ -2771,6 +2777,7 @@ static void migration_bitmap_clear_discarded_pages(RAMState *rs)
 
 static bool ram_init_bitmaps(RAMState *rs, Error **errp)
 {
+    Error *local_err = NULL;
     bool ret = true;
 
     qemu_mutex_lock_ramlist();
@@ -2783,7 +2790,13 @@ static bool ram_init_bitmaps(RAMState *rs, Error **errp)
             if (!ret) {
                 goto out_unlock;
             }
-            migration_bitmap_sync_precopy(false);
+            /*
+             * Bypass the RAMBlock dirty sync and still publish the
+             * notification.
+             */
+            if (precopy_notify(PRECOPY_NOTIFY_AFTER_BITMAP_SYNC, &local_err)) {
+                error_report_err(local_err);
+            }
         }
     }
 out_unlock:
-- 
2.27.0