[Mesa-dev] [PATCH v3] i965/gen6/gs: Handle case where a GS doesn't allocate VUE

[Iago Toral]

Thanks Andrii, this version looks good to me.

Mark: this change fixes a GPU hang in sandy bridge with geometry
shaders (the change itself affects a path in the driver that is only
executed in SNB with GS, so nothing else is affected). While I think
the change in here is correct according to the PRMs and in fact it
seems to fix the GPU hang reported in Bugzilla, since this is tinkering
with the way in which we allocate and free VUEs for SNB GS I believe
that if this breaks anything it might produce a GPU hang and in that
case I would rather not hang Jenkins for everyone else until you have a
chance to restore it, so in order to minimize that risk, could you run
this through Jenkins when you are available? If that is inconvenient
for you just let me know and I will send it myself late in my day on
Monday to minimize the risk.

Thanks,
Iago

On Fri, 2018-06-22 at 10:59 +0300, Andrii Simiklit wrote:
> We can not use the VUE Dereference flags combination for EOT
> message under ILK and SNB because the threads are not initialized
> there with initial VUE handle unlike Pre-IL.
> So to avoid GPU hangs on SNB and ILK we need
> to avoid usage of the VUE Dereference flags combination.
> (Was tested only on SNB but according to the specification
> SNB Volume 2 Part 1: 1.6.5.3, 1.6.5.6
> the ILK must behave itself in the similar way)
> 
> v2: Approach to fix this issue was changed.
> Instead of different EOT flags in the program end
> we will create VUE every time even if GS produces no output.
> 
> v3: Clean up the patch.
> Signed-off-by: Andrii Simiklit <andrii.simiklit at globallogic.com>
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105399
> 
> ---
>  src/intel/compiler/gen6_gs_visitor.cpp | 42 +++++++++++++++++-------
> ----------
>  1 file changed, 21 insertions(+), 21 deletions(-)
> 
> diff --git a/src/intel/compiler/gen6_gs_visitor.cpp
> b/src/intel/compiler/gen6_gs_visitor.cpp
> index 66c69fb..c9571cc 100644
> --- a/src/intel/compiler/gen6_gs_visitor.cpp
> +++ b/src/intel/compiler/gen6_gs_visitor.cpp
> @@ -350,27 +350,27 @@ gen6_gs_visitor::emit_thread_end()
>     int max_usable_mrf = FIRST_SPILL_MRF(devinfo->gen);
>  
>     /* Issue the FF_SYNC message and obtain the initial VUE handle.
> */
> +   this->current_annotation = "gen6 thread end: ff_sync";
> +
> +   vec4_instruction *inst = NULL;
> +   if (prog->info.has_transform_feedback_varyings) {
> +      src_reg sol_temp(this, glsl_type::uvec4_type);
> +      emit(GS_OPCODE_FF_SYNC_SET_PRIMITIVES,
> +           dst_reg(this->svbi),
> +           this->vertex_count,
> +           this->prim_count,
> +           sol_temp);
> +      inst = emit(GS_OPCODE_FF_SYNC,
> +                  dst_reg(this->temp), this->prim_count, this-
> >svbi);
> +   } else {
> +      inst = emit(GS_OPCODE_FF_SYNC,
> +                  dst_reg(this->temp), this->prim_count,
> brw_imm_ud(0u));
> +   }
> +   inst->base_mrf = base_mrf;
> +
>     emit(CMP(dst_null_ud(), this->vertex_count, brw_imm_ud(0u),
> BRW_CONDITIONAL_G));
>     emit(IF(BRW_PREDICATE_NORMAL));
>     {
> -      this->current_annotation = "gen6 thread end: ff_sync";
> -
> -      vec4_instruction *inst;
> -      if (prog->info.has_transform_feedback_varyings) {
> -         src_reg sol_temp(this, glsl_type::uvec4_type);
> -         emit(GS_OPCODE_FF_SYNC_SET_PRIMITIVES,
> -              dst_reg(this->svbi),
> -              this->vertex_count,
> -              this->prim_count,
> -              sol_temp);
> -         inst = emit(GS_OPCODE_FF_SYNC,
> -                     dst_reg(this->temp), this->prim_count, this-
> >svbi);
> -      } else {
> -         inst = emit(GS_OPCODE_FF_SYNC,
> -                     dst_reg(this->temp), this->prim_count,
> brw_imm_ud(0u));
> -      }
> -      inst->base_mrf = base_mrf;
> -
>        /* Loop over all buffered vertices and emit URB write messages
> */
>        this->current_annotation = "gen6 thread end: urb writes init";
>        src_reg vertex(this, glsl_type::uint_type);
> @@ -414,7 +414,7 @@ gen6_gs_visitor::emit_thread_end()
>                 dst_reg reg = dst_reg(MRF, mrf);
>                 reg.type = output_reg[varying][0].type;
>                 data.type = reg.type;
> -               vec4_instruction *inst = emit(MOV(reg, data));
> +               inst = emit(MOV(reg, data));
>                 inst->force_writemask_all = true;
>  
>                 mrf++;
> @@ -460,7 +460,7 @@ gen6_gs_visitor::emit_thread_end()
>      *
>      * However, this would lead us to end the program with an ENDIF
> opcode,
>      * which we want to avoid, so what we do is that we always
> request a new
> -    * VUE handle every time we do a URB WRITE, even for the last
> vertex we emit.
> +    * VUE handle every time, even if GS produces no output.
>      * With this we make sure that whether we have emitted at least
> one vertex
>      * or none at all, we have to finish the thread without writing
> to the URB,
>      * which works for both cases by setting the COMPLETE and UNUSED
> flags in
> @@ -476,7 +476,7 @@ gen6_gs_visitor::emit_thread_end()
>        emit(GS_OPCODE_SET_DWORD_2, dst_reg(MRF, base_mrf), data);
>     }
>  
> -   vec4_instruction *inst = emit(GS_OPCODE_THREAD_END);
> +   inst = emit(GS_OPCODE_THREAD_END);
>     inst->urb_write_flags = BRW_URB_WRITE_COMPLETE |
> BRW_URB_WRITE_UNUSED;
>     inst->base_mrf = base_mrf;
>     inst->mlen = 1;