migration/postcopy: Send device states without copying buffer

Put buffer can be async as long as the flush happens before the buffer will
be recycled / reused.  Do it for postcopy package data.  Quick measurement
shows a small VM the time to push / flush the package shrinks from 91us to
38us.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Tested-by: Lukas Straub <lukasstraub2@web.de>
Link: https://lore.kernel.org/qemu-devel/20260127185254.3954634-14-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>

diff --git a/migration/savevm.c b/migration/savevm.c
index 9d2109718ac7de50f47ced4c110aa27ba7085229..d41e89228d6f1618de83fc3c604eb73953b19918 100644 (file)
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1136,7 +1136,8 @@ int qemu_savevm_send_packaged(QEMUFile *f, const uint8_t *buf, size_t len)
     trace_qemu_savevm_send_packaged();
     qemu_savevm_command_send(f, MIG_CMD_PACKAGED, 4, (uint8_t *)&tmp);
 
-    qemu_put_buffer(f, buf, len);
+    /* We can use async put because the qemufile will be flushed right away */
+    qemu_put_buffer_async(f, buf, len, false);
     qemu_fflush(f);
 
     return 0;