[Mesa-dev] [PATCH v2 3/3] mapi/glthread: generate asynchronous code for PBO transfer

[gregory hainaut]

On Thu, 13 Apr 2017 18:31:06 +0200
Nicolai Hähnle <nhaehnle at gmail.com> wrote:

> On 05.04.2017 12:30, Gregory Hainaut wrote:
> >              # Classify fixed and variable parameters.
> >              self.fixed_params = []
> >              self.variable_params = []
> >              for p in self.parameters:
> >                  if p.is_padding:
> >                      continue
> >     -            if p.is_variable_length():
> >     +            if self.marshal == "upbo" and p.is_pointer():
> >     +                # Pixel buffer transfer API is tricky. By default
> > it contains
> >     +                # a pointer to user memory so a variable length parameter.
> >     +                # When a pixel buffer is bound, the pointer
> > becomes an offset.
> >     +                #
> >     +                # Non-PBO transfer will be synchronous so
> > parameter type isn't
> >     +                # important. PBO transfer will be asynchronous so
> > the parameter
> >     +                # must be marked as fixed
> >     +                self.fixed_params.append(p)
> >
> >
> >> If this is needed for upbo, shouldn't it also be needed for ppbo?
> >>
> >> Cheers,
> >> Nicolai
> >
> > Hello Nicolai,
> >
> > It isn't symmetrical. In case of UPBO data ought to be copied from app
> > thread to gl thread. You can see variable_length parameter as input
> > pointer. Variable length will generate the memcpy code.
> >
> > However PPBO will copy from GPU to user pointer. There is no data
> > associated with the pointer so the pointer isn't "used" by glthread,
> > only transferred to GL.
> >
> > I think the code would love an extra comment.
> 
> Okay, I get it now. But the comment could maybe use some re-wording, 
> especially because this whole issue only applies to some functions: 
> those where the marshaling code theoretically has a size, such as with 
> glCompressedTexImage2D. It would be good to clarify that.

Yes. I added this comment. Though I'm not sure it enough.

+ # variable_params are meaningful when pointers are associated
+ # with a payload hence it only impacts upbo but not ppbo.

Cheers,
Gregory

> 
> Thanks,
> Nicolai