Re: [RFC 3/8] virtio: Add API to batch set host notifiers

[Greg Kurz]

On Tue, 30 Mar 2021 14:55:42 +0100
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> On Tue, Mar 30, 2021 at 12:17:40PM +0200, Greg Kurz wrote:
> > On Mon, 29 Mar 2021 18:10:57 +0100
> > Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > > On Thu, Mar 25, 2021 at 04:07:30PM +0100, Greg Kurz wrote:
> > > > @@ -315,6 +338,10 @@ static void 
> > > > virtio_bus_unset_and_cleanup_host_notifiers(VirtioBusState *bus,
> > > >  
> > > >      for (i = 0; i < nvqs; i++) {
> > > >          virtio_bus_set_host_notifier(bus, i + n_offset, false);
> > > > +    }
> > > > +    /* Let address_space_update_ioeventfds() run before closing 
> > > > ioeventfds */
> > > 
> > > assert(memory_region_transaction_depth == 0)?
> > > 
> > 
> > Hmm... appart from the fact that memory_region_transaction_depth is
> > a memory internal thing that shouldn't be exposed here, it seems to
> > me that memory_region_transaction_depth can be != 0 when, e.g. when
> > batching is used... or I'm missing something ?
> > 
> > I was actually thinking of adding some asserts for that in the
> > memory_region_*_eventfd_full() functions introduced by patch 1.
> > 
> >     if (!transaction) {
> >         memory_region_transaction_begin();
> >     }
> >     assert(memory_region_transaction_depth != 0);
> 
> In that case is it safe to call virtio_bus_cleanup_host_notifier()
> below? I thought it depends on the transaction committing first.
> 

Yes because the transaction ends...

> > 
> > > > +    virtio_bus_set_host_notifier_commit(bus);
...                here ^^

> > > > +    for (i = 0; i < nvqs; i++) {
> > > >          virtio_bus_cleanup_host_notifier(bus, i + n_offset);
> > > >      }
> > > >  }

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