migration/block: Avoid invoking blk_drain too frequently

Increase bmds->cur_dirty after submit io, so reduce the frequency
involve into blk_drain, and improve the performance obviously
when block migration.

The performance test result of this patch:

During the block dirty save phase, this patch improve guest os IOPS
from 4.0K to 9.5K. and improve the migration speed from
505856 rsec/s to 855756 rsec/s.

Signed-off-by: Lidong Chen <jemmy858585@gmail.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

diff --git a/migration/block.c b/migration/block.c
index 67412282003500c45c5e74d38ee23e6041035203..7734ff728a57f9b919f1286fbba3ab074fedb054 100644 (file)
--- a/migration/block.c
+++ b/migration/block.c
@@ -576,6 +576,9 @@ static int mig_save_device_dirty(QEMUFile *f, BlkMigDevState *bmds,
             }
 
             bdrv_reset_dirty_bitmap(bmds->dirty_bitmap, sector, nr_sectors);
+            sector += nr_sectors;
+            bmds->cur_dirty = sector;
+
             break;
         }
         sector += BDRV_SECTORS_PER_DIRTY_CHUNK;