On 25 Sep 2013, at 13:15, Stefan Hajnoczi wrote: > 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 The outdated FIXME comment can be removed.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. > > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
Signed-off-by: Alex Bligh <a...@alex.org.uk> (if I meant 'Reviewed-By:' please change it!) > --- > block.c | 7 +------ > 1 file changed, 1 insertion(+), 6 deletions(-) > > diff --git a/block.c b/block.c > index ea4956d..5b276fb 100644 > --- a/block.c > +++ b/block.c > @@ -1558,13 +1558,8 @@ void bdrv_drain_all(void) > 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(); > -- > 1.8.3.1 > > > -- Alex Bligh