Re: [PATCH v5 0/6] block/rbd: migrate to coroutines and add write zeroes support

[Peter Lieven]

Am 09.07.21 um 12:21 schrieb Kevin Wolf:
> Am 08.07.2021 um 20:23 hat Peter Lieven geschrieben:
> > Am 08.07.2021 um 14:18 schrieb Kevin Wolf <kwolf@redhat.com>:
> > > Am 07.07.2021 um 20:13 hat Peter Lieven geschrieben:
> > > > > Am 06.07.2021 um 17:25 schrieb Kevin Wolf <kwolf@redhat.com>:
> > > > > Am 06.07.2021 um 16:55 hat Peter Lieven geschrieben:
> > > > > > I will have a decent look after my vacation.
> > > > > Sounds good, thanks. Enjoy your vacation!
> > > > As I had to fire up my laptop to look into another issue anyway, I
> > > > have sent two patches for updating MAINTAINERS and to fix the int vs.
> > > > bool mix for task->complete.
> > > I think you need to reevaluate your definition of vacation. ;-)
> > Lets talk about this when the kids are grown up. Sometimes sending
> > patches can be quite relaxing :-)
> Heh, fair enough. :-)
>
> > > But thanks anyway.
> > >
> > > > As Paolos fix (5f50be9b5) is relatively new and there are maybe other
> > > > non obvious problems when removing the BH indirection and we are close
> > > > to soft freeze I would leave the BH removal change for 6.2.
> > > Sure, code cleanups aren't urgent.
> > Isn’t the indirection also a slight performance drop?
> Yeah, I guess technically it is, though I doubt it's measurable.


As promised I was trying to remove the indirection through the BH after Qemu 
6.1 release.

However, if I remove the BH I run into the following assertion while running 
some fio tests:


qemu-system-x86_64: ../block/block-backend.c:1197: blk_wait_while_drained: Assertion 
`blk->in_flight > 0' failed.


Any idea?


This is what I changed:


diff --git a/block/rbd.c b/block/rbd.c
index 3cb24f9981..bc1dbc20f7 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -1063,13 +1063,6 @@ static int qemu_rbd_resize(BlockDriverState *bs, 
uint64_t size)
     return 0;
 }

-static void qemu_rbd_finish_bh(void *opaque)
-{
-    RBDTask *task = opaque;
-    task->complete = true;
-    aio_co_wake(task->co);
-}
-
 /*
  * This is the completion callback function for all rbd aio calls
  * started from qemu_rbd_start_co().
@@ -1083,8 +1076,8 @@ static void qemu_rbd_completion_cb(rbd_completion_t c, 
RBDTask *task)
 {
     task->ret = rbd_aio_get_return_value(c);
     rbd_aio_release(c);
-    aio_bh_schedule_oneshot(bdrv_get_aio_context(task->bs),
-                            qemu_rbd_finish_bh, task);
+    task->complete = true;
+    aio_co_wake(task->co);
 }


Peter