Re: [Qemu-devel] [PATCH v4 0/2] virtio: Move host features to backends

[Michael S. Tsirkin]

On Tue, Apr 28, 2015 at 08:14:44PM +0200, Michael S. Tsirkin wrote:
> On Tue, Apr 28, 2015 at 04:35:16PM +0200, Michael S. Tsirkin wrote:
> > On Tue, Apr 28, 2015 at 03:24:19PM +0200, Cornelia Huck wrote:
> > > On Tue, 28 Apr 2015 14:16:40 +0100
> > > Peter Maydell <address@hidden> wrote:
> > > 
> > > > On 28 April 2015 at 14:13, Michael S. Tsirkin <address@hidden> wrote:
> > > > > The patches look correct to me too, but I want s390
> > > > > cleaned up so it does not include COMMON_FEATURES
> > > > > in 100 places, and I prefer merging it all together.
> > > > 
> > > > It seems a bit harsh to ask Shannon to do s390 cleanup when
> > > > he doesn't have any access to s390 guests or test cases...
> > > > Making S390 put COMMON_FEATURES in the right places seems
> > > > to me like a separate bit of s390-specific cleanup.
> > > 
> > > Yep, see my other reply... I'm not quite sure what's wrong with
> > > event_idx on virtio-blk for s390-virtio, or I would gladly make this
> > > consistent with the other transports. Any hints appreciated :)
> > 
> > Is this still happening?
> > 
> > It is possible that what was missing was
> > 92045d80badc43c9f95897aad675dc7ef17a3b3f
> > and/or
> > a281ebc11a6917fbc27e1a93bb5772cd14e241fc
> > 
> 
> Found this:
> http://thread.gmane.org/gmane.comp.emulators.qemu/280334/focus=280357
> so it's unlikely: these commits are from 2012, you saw
> issues in 2014.
> 
> We really need to fix it. virtio 1 work will be much easier if
> we can just move features into virtio dev.

I'm beginning to suspect this is a wrong implementation of barriers.
Questions:
    - which compiler to you use?
    - can you pls disassemble code for smp_wmb smp_rmb and smp_mb?
      They all must do br %r14 I think, and this is what
      s390x-linux-gnu-gcc generated for me:
        s390x-linux-gnu-gcc (GCC) 4.9.1

> > -- 
> > MST