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, 24 insertions, 16 deletions

diff --git a/migration/ram.c b/migration/ram.c
index 5379164..f4cd903 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -425,18 +425,25 @@ uint64_t ram_bytes_remaining(void)
                        0;
 }
 
+/*
+ * NOTE: not all stats in ram_counters are used in reality.  See comments
+ * for struct MigrationAtomicStats.  The ultimate result of ram migration
+ * counters will be a merged version with both ram_counters and the atomic
+ * fields in ram_atomic_counters.
+ */
 MigrationStats ram_counters;
+MigrationAtomicStats ram_atomic_counters;
 
 void ram_transferred_add(uint64_t bytes)
 {
     if (runstate_is_running()) {
         ram_counters.precopy_bytes += bytes;
     } else if (migration_in_postcopy()) {
-        ram_counters.postcopy_bytes += bytes;
+        stat64_add(&ram_atomic_counters.postcopy_bytes, bytes);
     } else {
         ram_counters.downtime_bytes += bytes;
     }
-    ram_counters.transferred += bytes;
+    stat64_add(&ram_atomic_counters.transferred, bytes);
 }
 
 void dirty_sync_missed_zero_copy(void)
@@ -725,7 +732,7 @@ void mig_throttle_counter_reset(void)
 
     rs->time_last_bitmap_sync = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
     rs->num_dirty_pages_period = 0;
-    rs->bytes_xfer_prev = ram_counters.transferred;
+    rs->bytes_xfer_prev = stat64_get(&ram_atomic_counters.transferred);
 }
 
 /**
@@ -1085,8 +1092,9 @@ uint64_t ram_pagesize_summary(void)
 
 uint64_t ram_get_total_transferred_pages(void)
 {
-    return  ram_counters.normal + ram_counters.duplicate +
-                compression_counters.pages + xbzrle_counters.pages;
+    return  stat64_get(&ram_atomic_counters.normal) +
+        stat64_get(&ram_atomic_counters.duplicate) +
+        compression_counters.pages + xbzrle_counters.pages;
 }
 
 static void migration_update_rates(RAMState *rs, int64_t end_time)
@@ -1145,8 +1153,8 @@ static void migration_trigger_throttle(RAMState *rs)
 {
     MigrationState *s = migrate_get_current();
     uint64_t threshold = s->parameters.throttle_trigger_threshold;
-
-    uint64_t bytes_xfer_period = ram_counters.transferred - rs->bytes_xfer_prev;
+    uint64_t bytes_xfer_period =
+        stat64_get(&ram_atomic_counters.transferred) - rs->bytes_xfer_prev;
     uint64_t bytes_dirty_period = rs->num_dirty_pages_period * TARGET_PAGE_SIZE;
     uint64_t bytes_dirty_threshold = bytes_xfer_period * threshold / 100;
 
@@ -1209,7 +1217,7 @@ static void migration_bitmap_sync(RAMState *rs)
         /* reset period counters */
         rs->time_last_bitmap_sync = end_time;
         rs->num_dirty_pages_period = 0;
-        rs->bytes_xfer_prev = ram_counters.transferred;
+        rs->bytes_xfer_prev = stat64_get(&ram_atomic_counters.transferred);
     }
     if (migrate_use_events()) {
         qapi_event_send_migration_pass(ram_counters.dirty_sync_count);
@@ -1285,7 +1293,7 @@ static int save_zero_page(RAMState *rs, RAMBlock *block, ram_addr_t offset)
     int len = save_zero_page_to_file(rs, rs->f, block, offset);
 
     if (len) {
-        ram_counters.duplicate++;
+        stat64_add(&ram_atomic_counters.duplicate, 1);
         ram_transferred_add(len);
         return 1;
     }
@@ -1322,9 +1330,9 @@ static bool control_save_page(RAMState *rs, RAMBlock *block, ram_addr_t offset,
     }
 
     if (bytes_xmit > 0) {
-        ram_counters.normal++;
+        stat64_add(&ram_atomic_counters.normal, 1);
     } else if (bytes_xmit == 0) {
-        ram_counters.duplicate++;
+        stat64_add(&ram_atomic_counters.duplicate, 1);
     }
 
     return true;
@@ -1354,7 +1362,7 @@ static int save_normal_page(RAMState *rs, RAMBlock *block, ram_addr_t offset,
         qemu_put_buffer(rs->f, buf, TARGET_PAGE_SIZE);
     }
     ram_transferred_add(TARGET_PAGE_SIZE);
-    ram_counters.normal++;
+    stat64_add(&ram_atomic_counters.normal, 1);
     return 1;
 }
 
@@ -1410,7 +1418,7 @@ static int ram_save_multifd_page(RAMState *rs, RAMBlock *block,
     if (multifd_queue_page(rs->f, block, offset) < 0) {
         return -1;
     }
-    ram_counters.normal++;
+    stat64_add(&ram_atomic_counters.normal, 1);
 
     return 1;
 }
@@ -1448,7 +1456,7 @@ update_compress_thread_counts(const CompressParam *param, int bytes_xmit)
     ram_transferred_add(bytes_xmit);
 
     if (param->zero_page) {
-        ram_counters.duplicate++;
+        stat64_add(&ram_atomic_counters.duplicate, 1);
         return;
     }
 
@@ -2623,9 +2631,9 @@ void acct_update_position(QEMUFile *f, size_t size, bool zero)
     uint64_t pages = size / TARGET_PAGE_SIZE;
 
     if (zero) {
-        ram_counters.duplicate += pages;
+        stat64_add(&ram_atomic_counters.duplicate, pages);
     } else {
-        ram_counters.normal += pages;
+        stat64_add(&ram_atomic_counters.normal, pages);
         ram_transferred_add(size);
         qemu_file_credit_transfer(f, size);
     }