On Fri, Mar 15, 2019 at 8:21 AM Axel Davy <davyax...@gmail.com> wrote: > > On 15/03/2019 13:12, Rob Clark wrote: > > On Fri, Mar 15, 2019 at 3:49 AM Axel Davy <davyax...@gmail.com> wrote: > > >> To my knowledge, the semantic of set_sampler_views was changed two years > >> ago, and that caused some issues: > >> https://github.com/iXit/Mesa-3D/issues/308 > >> > >> Making drivers consistent (and complete the doc) is a good initiative. > >> > >> My understanding though is that some drivers may want different > >> behaviors in order to reduce overhead. If I understood correctly, > >> radeonsi prefers to minimize view changes to reduce cpu overhead (and > >> thus prefers not to unbind things outside of the set_sampler_views call > >> range), > >> while nouveau prefers to have only what's needed by the call bound for > >> better gpu performance. I think both are happy with the current code, > >> because the latter preferred behavior can be emulated in the driver, > >> while it would be more difficult for the former. > > Hmm, but this is at odds with Roland's statement that sampler views > > outside the specified range are unmodified. > > > > If we defined the API such that slots >= start+nr are unbound, then a > > driver could choose not to touch them to minimize CPU overhead. But > > if defined that they are unmodified then the driver cannot silently > > discard them. > > > > BR, > > -R > > > The sampler views outside the specified range are unmodified. > This is compatible with what I said. Nouveau determines the minimum > number of samplers actually needed > by the current shader, and internally unbinds those above (and rebinds > if needed by new shader). >
Mmmm, unless there is something subtle that I'm overlooking, I'm not sure that I agree.. nvc0_stage_set_sampler_views() unref's the remaining sampler views. The end result is what you describe, but only because of an implementation detail of how mesa/st works (ie. it rebinds them if needed for a new shader). But as Ilia mentioned, I see the use in differentiating between active and bound. Thas might be a good argument to switch back to my initial docs patch which defined slots >= nr+count as unbound. (otoh, nouveau could just track a bitmask of samplers used by the shader internally, I guess?) BR, -R _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
