migration: calculate expected_downtime

We removed the calculation in commit e4ed1541

Now we add it back.  We need to create dirty_bytes_rate because we
can't include cpu-all.h from migration.c, and there is no other way to
include TARGET_PAGE_SIZE.
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Reviewed-by: NOrit Wasserman <owasserm@redhat.com>

arch_init.c

@@ -414,6 +414,7 @@ static void migration_bitmap_sync(void)
     if (end_time > start_time + 1000) {
         s->dirty_pages_rate = num_dirty_pages_period * 1000
             / (end_time - start_time);
+        s->dirty_bytes_rate = s->dirty_pages_rate * TARGET_PAGE_SIZE;
         start_time = end_time;
         num_dirty_pages_period = 0;
     }

include/migration/migration.h

@@ -51,6 +51,7 @@ struct MigrationState
     int64_t downtime;
     int64_t expected_downtime;
     int64_t dirty_pages_rate;
+    int64_t dirty_bytes_rate;
     bool enabled_capabilities[MIGRATION_CAPABILITY_MAX];
     int64_t xbzrle_cache_size;
     bool complete;

migration.c

@@ -738,6 +738,11 @@ static void *buffered_file_thread(void *opaque)
             DPRINTF("transferred %" PRIu64 " time_spent %" PRIu64
                     " bandwidth %g max_size %" PRId64 "\n",
                     transferred_bytes, time_spent, bandwidth, max_size);
+            /* if we haven't sent anything, we don't want to recalculate
+               10000 is a small enough number for our purposes */
+            if (s->dirty_bytes_rate && transferred_bytes > 10000) {
+                s->expected_downtime = s->dirty_bytes_rate / bandwidth;
+            }
 
             s->bytes_xfer = 0;
             sleep_time = 0;