[Qemu-devel] [PATCH v4 1/1] migration: calculate expected_downtime with ram_bytes_remaining()

[Balamuruhan S <bala24@linux.vnet.ibm.com>]

expected_downtime value is not accurate with dirty_pages_rate * page_size,
using ram_bytes_remaining() would yeild it resonable.

consider to read the remaining ram just after having updated the dirty
pages count later migration_bitmap_sync_range() in migration_bitmap_sync()
and reuse the `remaining` field in ram_counters to hold ram_bytes_remaining()
for calculating expected_downtime.

Reported-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Balamuruhan S <bala24@linux.vnet.ibm.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 migration/migration.c | 3 +--
 migration/ram.c       | 1 +
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index ea9a6cbb87..cb14dadb26 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2739,8 +2739,7 @@ static void migration_update_counters(MigrationState *s,
      * recalculate. 10000 is a small enough number for our purposes
      */
     if (ram_counters.dirty_pages_rate && transferred > 10000) {
-        s->expected_downtime = ram_counters.dirty_pages_rate *
-            qemu_target_page_size() / bandwidth;
+        s->expected_downtime = ram_counters.remaining / bandwidth;
     }
 
     qemu_file_reset_rate_limit(s->to_dst_file);
diff --git a/migration/ram.c b/migration/ram.c
index a500015a2f..a94a2b829e 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1159,6 +1159,7 @@ static void migration_bitmap_sync(RAMState *rs)
     RAMBLOCK_FOREACH_MIGRATABLE(block) {
         migration_bitmap_sync_range(rs, block, 0, block->used_length);
     }
+    ram_counters.remaining = ram_bytes_remaining();
     rcu_read_unlock();
     qemu_mutex_unlock(&rs->bitmap_mutex);
 
-- 
2.14.3