Re: [Qemu-devel] [PATCH 3/3] virtio: set ISR on dataplane notifications

[Michael S. Tsirkin]

On Tue, Nov 15, 2016 at 11:21:55AM -0700, Alex Williamson wrote:
> On Tue, 15 Nov 2016 19:58:52 +0200
> "Michael S. Tsirkin" <address@hidden> wrote:
> 
> > On Tue, Nov 15, 2016 at 10:48:15AM -0700, Alex Williamson wrote:
> > > On Tue, 15 Nov 2016 19:38:30 +0200
> > > "Michael S. Tsirkin" <address@hidden> wrote:
> > >   
> > > > On Tue, Nov 15, 2016 at 05:22:49PM +0100, Paolo Bonzini wrote:  
> > > > > 
> > > > > 
> > > > > On 15/11/2016 16:44, Michael S. Tsirkin wrote:    
> > > > > > True. We could drop it from non-data plane, it's just that we never 
> > > > > > had
> > > > > > a reason to. vhost in kernel does not set ISR in MSI mode, either.  
> > > > > >   
> > > > > 
> > > > > Yeah, I suspected that.  But dropping it from non-dataplane would 
> > > > > break
> > > > > Windows hibernation and crashdump, just like it did for Alex.    
> > > > 
> > > > I guess it's just a question of updating the drivers,
> > > > isn't it? To me, hibernation/crashdump doesn't sound important
> > > > enough to warrant work-arounds, but if you feel otherwise,
> > > > I'm fine with doing this work-around for dataplane.  
> > > 
> > > The fact that Windows is trying to do some sort of hibernation is not
> > > visible to the user, I'm simply trying to shutdown the VM.  That's
> > > rather important on my scale of functionality.  If we have drivers in
> > > the wild doing this, does it matter what's in the spec?  
> > 
> > It matters that latest drivers are already OK. "Update drivers"
> > has been the advice for any kind of windows problem for years.
> > 
> > > Smells like a
> > > regression from an end user perspective. Thanks,
> > > 
> > > Alex  
> > 
> > This exposes a driver bug, yes. The right fix is easy to point
> > out, whether we want a work-around I'm not sure - I understand that
> > you feel strongly that we do, is that right? OK, just let's document
> > what's going on and which versions are affected.
> 
> I don't mind updating my drivers, I'm just guessing that the average
> user doesn't know what virtio driver version they're running, doesn't
> read release notes, and will be at least slightly annoyed by this
> behavior that looks and smells like a regression from v2.7.  If it
> hit me, then there are probably others affected as well.  It's up to you
> to weigh maintaining not-entirely-spec-complaint behavior vs user angst.
> Thanks,
> 
> Alex

I think I'll merge the work-around if it's better documented.
If you think it should go in, can you provide your tested-by tag?

-- 
MST