[virglrenderer-devel] multiprocess model and GL

[Gerd Hoffmann]

  Hi,

> > The problematic ones are the mesa-created virgl resources.  If the host
> > (and possibly the host gpu hardware too) can see any resource updates
> > before mesa explicitly calls the TRANSFER ioctl, would that break the
> > driver?  Or would mesa set the "you can use udmabufs" flag anyway on all
> > resources?
> Oh, mesa would break.  It relies on the existence of shadow buffers
> currently.  If there was a "you must use udmabuf" flag, mesa could
> theoretically use it and allocate staging buffers itself when needed.
> But if the flag was just a hint, it would not be enough.
> 
> There are also GL_PERSISTENT_BIT buffer objects.  Mesa does not
> support them now.  Mesa could use the "you can use udmabuf" flag to
> support them.  But the bit is usually set along with
> GL_MAP_COHERENT_BIT.  Mesa would still needs the "you must use
> udmabuf" flag.

Hmm, so far my plan is to have a "you can use dmabuf" flag only.

Would a "you must use udmabuf" flag useful?  If GL_PERSISTENT_BIT is
typically used together with GL_MAP_COHERENT_BIT I would expect mesa
would try to use hostmem anyway ...

cheers,
  Gerd