Am 25.11.2014 um 08:23 hat Ming Lei geschrieben: > Previously -EAGAIN is simply ignored for !s->io_q.plugged case, > and sometimes it is easy to cause -EIO to VM, such as NVME device. > > This patch handles -EAGAIN by io queue for !s->io_q.plugged case, > and it will be retried in following aio completion cb. > > Reviewed-by: Paolo Bonzini <pbonz...@redhat.com> > Suggested-by: Paolo Bonzini <pbonz...@redhat.com> > Signed-off-by: Ming Lei <ming....@canonical.com> > --- > block/linux-aio.c | 24 ++++++++++++++++-------- > 1 file changed, 16 insertions(+), 8 deletions(-) > > diff --git a/block/linux-aio.c b/block/linux-aio.c > index 11ac828..ac25722 100644 > --- a/block/linux-aio.c > +++ b/block/linux-aio.c > @@ -282,8 +282,13 @@ static int ioq_enqueue(struct qemu_laio_state *s, struct > iocb *iocb) > s->io_q.iocbs[idx++] = iocb; > s->io_q.idx = idx; > > - /* submit immediately if queue depth is above 2/3 */ > - if (idx > s->io_q.size * 2 / 3) { > + /* > + * This is reached in two cases: queue not plugged but io_submit > + * returned -EAGAIN, or queue plugged. In the latter case, start > + * submitting some I/O if the queue is getting too full. In the > + * former case, instead, wait until an I/O operation is completed. > + */
Are we guaranteed that an I/O operation is in flight when we get -EAGAIN? The manpage of io_submit isn't very clear on this, "insufficient resources" could be for any reason. Because otherwise we might not ever submit this request. > + if (s->io_q.plugged && unlikely(idx > s->io_q.size * 2 / 3)) { > ioq_submit(s); > } Kevin