block: clean up bdrv_drain_all() throttling comments
Since cc0681c45430a1f1a4c2d06e9499b7775afc9a18 ("block: Enable the new
throttling code in the block layer.") bdrv_drain_all() no longer spins.
The code used to look as follows:
do {
busy = qemu_aio_wait();
/* FIXME: We do not have timer support here, so this is effectively
* a busy wait.
*/
QTAILQ_FOREACH(bs, &bdrv_states, list) {
while (qemu_co_enter_next(&bs->throttled_reqs)) {
busy = true;
}
}
} while (busy);
Note that throttle requests are kicked but I/O throttling limits are
still in effect. The loop spins until the vm_clock time allows the
request to make progress and complete.
The new throttling code introduced bdrv_start_throttled_reqs(). This
function not only kicks throttled requests but also temporarily disables
throttling so requests can run.
The outdated FIXME comment can be removed. Also drop the busy = true
assignment since we overwrite it immediately afterwards.
Reviewed-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block.c b/block.c
index 1c83ef1..13f001a 100644
--- a/block.c
+++ b/block.c
@@ -1557,13 +1557,8 @@
BlockDriverState *bs;
while (busy) {
- /* FIXME: We do not have timer support here, so this is effectively
- * a busy wait.
- */
QTAILQ_FOREACH(bs, &bdrv_states, list) {
- if (bdrv_start_throttled_reqs(bs)) {
- busy = true;
- }
+ bdrv_start_throttled_reqs(bs);
}
busy = bdrv_requests_pending_all();
