Re: [PATCH] ui/gtk: skip any extra draw of same guest scanout blob res

[Dongwon Kim]

On Fri, Sep 17, 2021 at 12:02:02PM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > +    bool      draw_submitted;
> > +    QemuMutex mutex;
> 
> Why the mutex?  I think all the code runs while holding the BQL so it
> should be serialized.

Guest drawing process using blob is serialized (gd_egl_flush->scheduling
draw call->gd_egl_draw) but an asynchronous draw event from another thread
is causing a problem.

I initially thought using a flag (draw_submitted) would be enough to get this
worked around, but it wasn't as the asynchronous draw could take it over before,

dambuf->draw_submitted = false;

happens during normal draw sequence. I thought mutex would be a reasonable
solution for this case.

> 
> > +#ifdef CONFIG_GBM
> > +        if (dmabuf) {
> > +            qemu_mutex_lock(&dmabuf->mutex);
> > +            if (!dmabuf->draw_submitted) {
> > +                qemu_mutex_unlock(&dmabuf->mutex);
> > +                return;
> > +            } else {
> > +                dmabuf->draw_submitted = false;
> > +            }
> > +        }
> > +#endif
> 
> Factoring out that into helper functions is probably a good idea.  Then
> have stub functions for the CONFIG_GBM=no case and *alot* less #ifdefs
> in the code ...

I will look into this part.
Thanks,
DW

> 
> thanks,
>   Gerd
>