migration: Make dirty_bytes_last_sync atomic

As we set its value, it needs to be operated with atomics.
We rename it from remaining to better reflect its meaning.

Statistics always return the real reamaining bytes.  This was used to
store how much pages where dirty on the previous generation, so we can
calculate the expected downtime as: dirty_bytes_last_sync /
current_bandwith.

If we use the actual remaining bytes, we would see a very small value
at the end of the iteration.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
---

I am open to use ram_bytes_remaining() in its only use and be more
"optimistic" about the downtime.

Don't use __nocheck() functions.
Use stat64_get() now that it exists.

diff --git a/migration/migration.c b/migration/migration.c
index 9367bb2afc45f930e439b717badced04ea2e5ed0..abcadbb619e7b0dfb92e442c09645f4c615417de 100644 (file)
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2692,7 +2692,8 @@ static void migration_update_counters(MigrationState *s,
      */
     if (stat64_get(&ram_counters.dirty_pages_rate) &&
         transferred > 10000) {
-        s->expected_downtime = ram_counters.remaining / bandwidth;
+        s->expected_downtime =
+            stat64_get(&ram_counters.dirty_bytes_last_sync) / bandwidth;
     }
 
     qemu_file_reset_rate_limit(s->to_dst_file);

diff --git a/migration/ram.c b/migration/ram.c
index 5846f6e27fe5f601c2a100f3b985ae4a2dd63eb2..89be3e33204af7bc863baf8ca0c3f59d4d57d0ce 100644 (file)
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1224,7 +1224,7 @@ static void migration_bitmap_sync(RAMState *rs)
         RAMBLOCK_FOREACH_NOT_IGNORED(block) {
             ramblock_sync_dirty_bitmap(rs, block);
         }
-        ram_counters.remaining = ram_bytes_remaining();
+        stat64_set(&ram_counters.dirty_bytes_last_sync, ram_bytes_remaining());
     }
     qemu_mutex_unlock(&rs->bitmap_mutex);
 

diff --git a/migration/ram.h b/migration/ram.h
index f189cc79f84cf906390ad7b7a556f318730a92d6..04b05e1b2cf144946a55b6016e9b08346e78ec60 100644 (file)
--- a/migration/ram.h
+++ b/migration/ram.h
@@ -41,6 +41,7 @@
  * one thread).
  */
 typedef struct {
+    Stat64 dirty_bytes_last_sync;
     Stat64 dirty_pages_rate;
     Stat64 dirty_sync_count;
     Stat64 dirty_sync_missed_zero_copy;
@@ -51,7 +52,6 @@ typedef struct {
     Stat64 postcopy_bytes;
     Stat64 postcopy_requests;
     Stat64 precopy_bytes;
-    int64_t remaining;
     Stat64 transferred;
 } RAMStats;