migration: Use atomic ops properly for page accountings

To prepare for thread-safety on page accountings, at least below counters
need to be accessed only atomically, they are:

        ram_counters.transferred
        ram_counters.duplicate
        ram_counters.normal
        ram_counters.postcopy_bytes

There are a lot of other counters but they won't be accessed outside
migration thread, then they're still safe to be accessed without atomic
ops.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/migration/ram.h b/migration/ram.h
index 038d52f49f..81cbb0947c 100644
--- a/migration/ram.h
+++ b/migration/ram.h
@@ -32,7 +32,27 @@
 #include "qapi/qapi-types-migration.h"
 #include "exec/cpu-common.h"
 #include "io/channel.h"
+#include "qemu/stats64.h"
 
+/*
+ * These are the migration statistic counters that need to be updated using
+ * atomic ops (can be accessed by more than one thread).  Here since we
+ * cannot modify MigrationStats directly to use Stat64 as it was defined in
+ * the QAPI scheme, we define an internal structure to hold them, and we
+ * propagate the real values when QMP queries happen.
+ *
+ * IOW, the corresponding fields within ram_counters on these specific
+ * fields will be always zero and not being used at all; they're just
+ * placeholders to make it QAPI-compatible.
+ */
+typedef struct {
+    Stat64 transferred;
+    Stat64 duplicate;
+    Stat64 normal;
+    Stat64 postcopy_bytes;
+} MigrationAtomicStats;
+
+extern MigrationAtomicStats ram_atomic_counters;
 extern MigrationStats ram_counters;
 extern XBZRLECacheStats xbzrle_counters;
 extern CompressionStats compression_counters;